The promise of life was not a unique feature of the Old Covenant per se, but predated it and was included in the blessings promised to Abraham. (Gen.22:18) This promise was given by God on Mt. Moriah where Abraham offered Isaac up as a sacrifice. This later became the Temple Mount also called Zion, so the Psalmist could refer to it poetically this way...

Psa. 133:1-3
      ¹  Behold, how good and how pleasant it is
        For brethren to dwell together in unity!
     ²  It is like the precious oil upon the head,
        Running down on the beard,
        The beard of Aaron,
        Running down on the edge of his garments.
     3  It is like the dew of Hermon,
        Descending upon the mountains of Zion;
        For there Jehovah commanded the blessing--
        Life forevermore.     

    This promise actually predated everything, as it was in God's plan before he made the world.

Titus 1:1-2
Paul, a bondservant of God and an apostle of Jesus Christ, according to the faith of God’s elect and the acknowledgment of the truth which accords with godliness, in hope of eternal life which God, who cannot lie, promised before time began,

    In the Old Covenant time period, people were aware of the promise, but had little understanding of its full import because it was part of the mystery kept secret from the foundation of the world, not even angels being privy to it. (1Pet. 1:10-12) They, in faith were following a path to life.

Psa. 16:9-11
   ⁹  Therefore my heart is glad, and my glory rejoices;
      My flesh also will rest in hope.
  ¹⁰  For you will not leave my soul in Sheol,
       Nor will you allow your Holy One to see corruption.
  ¹¹ You will show me the path of life;
      In your presence is fullness of joy;
      At your right hand are pleasures forevermore.

Mt. 19:16-24
¹⁶  Now behold, one came and said to him, “Good teacher, what good thing shall I do that I may have eternal life?”
¹⁷  So he said to him, “Why do you call me good? No one is good but one, that is, God. But if you want to enter into life, keep the commandments.”
¹⁸  He said to him, “Which ones?” Jesus said, “You shall not murder,’ “You shall not commit adultery,’ “You shall not steal,’ “You shall not bear false witness,’
¹⁹  “Honor your father and your mother,’ and, “You shall love your neighbor as yourself.”’
²⁰  The young man said to him, “All these things I have kept from my youth. What do I still lack?”
²¹  Jesus said to him, “If you want to be perfect, go, sell what you have and give to the poor, and you will have treasure in heaven; and come, follow me.”
²²  But when the young man heard that saying, he went away sorrowful, for he had great possessions.
²³  Then Jesus said to his disciples, “Assuredly, I say to you that it is hard for a rich man to enter the kingdom of the heavens.
²⁴  And again I say to you, it is easier for a camel to go through the eye of a needle than for a rich man to enter the kingdom of God.”

    So here, eternal life (or entering into life) and perfection was to be found in a coming kingdom. The Jews sought for this. Jesus told them to pray, "Thy kingdom come..." Again, they were looking forward to it but not understanding the nature of this Eternal Life.

    It's amazing to me and very humbling, that the godly people of the Old Covenant all died in faith while not having received this Promise of Life.

Heb.11:11-16
¹¹ By faith Sarah herself also received strength to conceive seed, and she bore a child when she was past the age, because she judged him faithful who had promised.
¹² Therefore from one man, and him as good as dead, were born as many as the stars of the sky in multitude – innumerable as the sand which is by the seashore.
¹³ These all died in faith, not having received the promises, but having seen them afar off were
assured of them, embraced them and confessed that they were strangers and pilgrims on the earth.
¹⁴ For those who say such things declare plainly that they seek a homeland.
¹⁵ And truly if they had called to mind that country from which they had come out, they would have had opportunity to return.
¹⁶ But now they desire a better, that is, a heavenly country. Therefore God is not ashamed to be called their God, for he has prepared a city for them.

Heb.11:30-40
³⁰  By faith the walls of Jericho fell down after they were encircled for seven days.
³¹  By faith the harlot Rahab did not perish with those who did not believe, when she had received the spies with peace.
³²  And what more shall I say? For the time
would fail me to tell of Gideon and Barak and Samson and Jephthah, also of David and Samuel and the prophets:
³³  who through faith subdued kingdoms, worked righteousness, obtained promises, stopped the mouths of lions,
³⁴  quenched the violence of fire, escaped the edge of the sword, out of weakness were made strong, became valiant in battle, turned to flight the armies of the aliens.
³⁵  Women received their dead raised to life again.
Others were tortured, not accepting deliverance, that they might obtain a better resurrection.
³⁶  Still others had trial of mockings and scourgings, yes, and of chains and imprisonment.
³⁷  They were stoned, they were sawn in two, were tempted, were slain with the sword. They wandered about in sheepskins and goatskins, being destitute, afflicted, tormented –
³⁸  of whom the world was not worthy. They wandered in deserts and mountains, in dens and caves of the earth.
³⁹  And all these, having obtained a good testimony through faith, did not receive the promise,
⁴⁰  God having provided something better for us, that they apart from us should not be made perfect.

    Therefore we would have to conclude that those in the Old Covenant did not have spiritual life, they were not made complete. But they received it later when the kingdom came. That would be why God had them spend the time in Hades waiting for the fulfillment in Christ. Because having life is what is required to enter Heaven, and it was not until Christ came that the Life was revealed.
     "They, without us, should not be made complete". So they received the Eternal Life at the same time or after the first century Christians -- at the end of the age when the Promise was fulfilled. So when Christians first received eternal life, all the Old Covenant faithful also received it. We should cross reference Dan. 12:1-3, concerning the time of the great tribulation and the giving of everlasting life.

        Dan. 12:1-3
       ¹ "At that time Michael shall stand up,
        The great prince who stands watch over the sons of your people;
        And there shall be a time of trouble,
        Such as never was since there was a nation,
        Even to that time.
        And at that time your people shall be delivered,
        Every one who is found written in the book.
     ²  And many of those who sleep in the dust of the earth shall awake,
        Some to everlasting life,
        Some to shame and everlasting contempt.
     ³  Those who are wise shall shine
        Like the brightness of the firmament,
        And those who turn many to righteousness
        Like the stars forever and ever.

    So there was a resurrection just after the great tribulation (Mt. 24:21, 29-31) during the last days of the Jewish nation in the first century. There was a finishing up or a completion of the Old Covenant promises and prophesies.
     But some that are first shall be last and last shall be first. There seems to be several applications of this saying but I think Lk.13:30 may apply here, which reference, it seems, is of the same time period that Daniel spoke.

Lk. 13:24-30
²⁴  “Strive to enter through the narrow gate, for many, I say to you, will seek to enter and will not be able.
²⁵  When once the master of the house has risen up and shut the door, and you begin to stand outside and knock at the door, saying, “Lord, Lord, open for us,’ and he will answer and say to you, “I do not know you, where you are from,’
²⁶  then you will begin to say, “We ate and drank in your presence, and you taught in our streets.’
²⁷  But he will say, “I tell you I do not know you, where you are from. Depart from me, all you workers of iniquity.’
²⁸  There will be weeping and gnashing of teeth, when you see Abraham and Isaac and Jacob and all the prophets in the kingdom of God, and yourselves thrust out.
²⁹  They will come from the east and the west, from the north and the south, and sit down in the kingdom of God.
³⁰  And indeed there are last who will be first, and there are first who will be last.”

    It seems that some faithful from the beginning of the world who had been in Hades up to the time of Christ, at the consummation of the ages, would be last to receive Eternal Life in Christ; and others who are saved at the last hour at the very closing of the age, receive the same gift of Eternal Life that was promised to those who came before. So they were last to experience the world but first to go into the Kingdom.
    This could also be taken morally -- the Jews, first in prominence, but they would lose the race, coming in last place, and those of faith who are accounted as last, will be first of all and win the victory.
    One of the important things about this passage is the spanning of time to include the known dead in Hades with the people still living during the ministry of Jesus with their entrance into the new kingdom of God. This is when the Old Covenant people of faith were made complete along with the faithful of the New Covenant.

IV ) The Promise of Life was fulfilled by Jesus

    Of course, that "better thing" that God provided for us is the first fruits of the Spirit that the first century Christians received. Life, real and abundant, spiritual life, did not come until Christ came and gave himself for the life of the world.
    Jesus is constantly telling the Jews that he has brought life and can give it to them if they would only come to him and believe.

Jno. 6:31-35; 47-51
³¹  'Our fathers ate the manna in the desert; as it is written, “He gave them bread from heaven to eat.”’
³²  Then Jesus said to them, “Most assuredly, I say to you, Moses did not give you the bread from heaven, but my father gives you the true bread from heaven.
³³  For the bread of God is he who comes down from heaven and gives life to the world.”
³⁴  Then they said to him, “Lord, give us this bread always.”
³⁵  And Jesus said to them, “I am the bread of life. He who comes to me shall never hunger, and he who believes in me shall never thirst.

⁴⁷  Most assuredly, I say to you, he who believes in me has everlasting life.
⁴⁸  I am the bread of life.
⁴⁹  Your fathers ate the manna in the wilderness, and are dead.
⁵⁰  This is the bread which comes down from heaven, that one may eat of it and not die.
⁵¹  I am the living bread which came down from heaven. If anyone eats of this bread, he will live forever; and the bread that I shall give is my flesh, which I shall give for the life of the world.”

    Jesus came that they might have life and have it more abundantly. (Jno. 10:10) This is what he offered the Jews in the gift of the Holy Spirit, when the Spirit would come and quicken them to newness of spiritual life.

Jno. 7:37-39
³⁷ On the last day, that great day of the feast, Jesus stood and cried out, saying, “If anyone thirsts, let him come to me and drink.
³⁸  He who believes in me, as the scripture has said, out of his belly will flow rivers of living water.”
³⁹  But this he said concerning the Spirit, whom those believing in him were about to receive; for the Spirit was not yet [given], because Jesus was not yet glorified.

    It is the Spirit that gives life. (2Cor. 3:6) This is what is offered in Christ and was not available in the Old Covenant.

2Tim.1:8-10
⁸  Therefore do not be ashamed of the testimony of our Lord, nor of me his prisoner, but share with me in the sufferings for the gospel according to the power of God,
⁹  who has saved us and called us with a holy calling, not according to our works, but according to his own purpose and grace which was given to us in Christ Jesus before time began,
¹⁰  but has now been revealed by the appearing of our Savior Jesus Christ, who has abolished death and brought life and immortality to light through the gospel,

    This blessing that was promised was not seen until the gospel was preached in the first century.

V ) The power of his resurrection

In Phil.3:8-11 Paul wanted to know the power of Christ's resurrection. This power is something that has been working in us since we obeyed the gospel but something with which we may be unfamiliar, given the teaching that has been done in the church generally.

Eph.1:15-20
¹⁵  Therefore I also, after I heard of your faith in the Lord Jesus and your love for all the saints,
¹⁶  do not cease to give thanks for you, making mention of you in my prayers:
¹⁷  that the God of our Lord Jesus Christ, the Father of glory, may give to you the spirit of wisdom and revelation in the knowledge of him,
¹⁸  the eyes of your understanding being enlightened; that you may know what is the hope of his calling, what are the riches of the glory of his inheritance in the saints,
¹⁹  and what is the exceeding greatness of his power toward us who believe, according to the working of his mighty power
²⁰  which he worked in Christ when he raised him from the dead and seated him at his right hand in the heavenly places,

    This same power that is in us who believe is the same power whereby God raised Jesus from the dead, which is why it is called the power of his resurrection. Paul was speaking to Christians and he was praying that they might understand what this power is.

Eph.2:1; 4-6  (notice that "together" means along with him)
¹ And you he made alive, who were dead in trespasses and sins,

⁴ But God, who is rich in mercy, because of his great love with which he loved us,
⁵ even when we were dead in trespasses, made us alive together with Christ (by grace you have been saved),
⁶ and raised us up together, and made us sit together in the heavenly realm in Christ Jesus,

    The power of his resurrection begins in us by the new life that is quickened in us when we are raised from baptism in the likeness of his resurrection, to walk in newness of life. (Rom.6) It is the power of the new birth. The same power that raised Jesus from the dead is the same power that raises our spirits from the dead and quickens in us that new creation, the new man that is renewed in knowledge after the image of Jesus Christ. (Col.3:10)
    This principle and rule of Life in Christ, is to what I think Paul refers in Rom.5:10-18:

Rom.5:10
¹⁰  For if when we were enemies we were reconciled to God through the death of his son, much more, having been reconciled, we shall be saved by his life.

    I am reconciled by his death because his blood on the cross takes away my sin and I can lift up my head now and draw near to God because I am free from guilt.
    I am saved by his life because his resurrected life is the life that I can live now through his Spirit and be free from the dominion of sin in my life, and free from the death that was waiting to seal my fate. That is the Power of his resurrection.

5:17
¹⁷  For if by the one man’s offense death reigned through the one, much more those who receive abundance of grace and of the gift of righteousness will reign in life through the one, Jesus Christ.

    He is not talking about reigning in this life. He is saying that Life is the principle by which we reign in Jesus Christ. That is why it is called "justification of Life.

v.18
¹⁸  Therefore, as through one man’s offense judgment came to all men, resulting in condemnation, even so through one man’s righteous act the free gift came to all men, resulting in justification of life.

    Speaking of his resurrection, Jesus said in Jno.14:19, "Because I live, you shall live also."
    That is the power of his resurrection.

    We know the true life, the abundant life that Jesus gives us, when we know the power of his resurrection. It is the power of his resurrected life that makes our spiritual life possible.
    The sanctification of the Spirit is by Christ's life also. Because it is the Spirit's job to communicate Christ's holy life to us and form us into his image by faith. (Rom.8:2) The life of Jesus is not just raw power, but has an intrinsic nature of holiness. His life has a holy character which is the means by which we overcome sin toward sanctification. Our spiritual life is his life given to us. Christ's resurrection to life - the power of it - touches every aspect of the Christian's life.

VI ) How does One get this Life?

    Jesus said that you must believe in him to have everlasting life. Our faith in him becomes the acceptance of this gift of eternal life, (He says he gives it and I believe that I have it). Our faith is also the active response of our hearts in appropriating that new life - what people in the church generally refer to as obedience, (acting upon it as real).
    When we, by faith, come to him accepting his death for our forgiveness and trusting in him to give us a new life - then he, by his working and power, makes us spiritually alive.

Col. 2:11-13
¹¹  In him you were also circumcised with the circumcision made without hands, by putting off the body of the sins of the flesh, by the circumcision of Christ,
¹²  buried with him in immersion, in which you were also raised with him through faith in the working of God, who raised him from the dead.
¹³  And you, being dead in your trespasses and the uncircumcision of your flesh, he has made alive together with him, having forgiven you all trespasses,

    The working of God in immersion is that he forgives all our trespasses (for the remission of sins, Acts 2:38) and then he makes us alive spiritually, which is the new birth, (born of water and the Spirit, Jno.3:5). It is our faith in the "operation of God" that is essential in immersion. We are born again.
    Jesus explains all this to a Jew who was waiting for the promise.

Jno. 3:5-8
⁵  Jesus answered, “Most assuredly, I say to you, unless one is born of water and the Spirit, he cannot enter the kingdom of God.
⁶  That which is born of the flesh is flesh, and that which is born of the Spirit is spirit.
⁷  Do not marvel that I said to you, “You must be born again.’
⁸  The wind blows where it wishes, and you hear the sound of it, but cannot tell where it comes from and where it goes. So is everyone who is born of the Spirit.”

    Nicodemus still had his thoughts on the carnal plane. Jesus is explaining that true life is in the spirit - which necessitates a spiritual birth. This happens in immersion. We there begin to have spiritual life, because a relationship is thus established whereby we can know God, and to know God, is eternal life. (Jno.17:3)

Gal. 3:26-29
²⁶  For you are all sons of God through faith in Christ Jesus.
²⁷  For as many of you as were immersed into Christ have put on Christ.
²⁸  There is neither Jew nor Greek, there is neither slave nor free, there is neither male nor female; for you are all one in Christ Jesus.
²⁹  And if you are Christ’s, then you are Abraham’s seed, and heirs according to the promise.

Gal. 4:4-9
⁴  But when the fullness of the time had come, God sent forth his Son, born of a woman, born under law,
⁵  to redeem those who were under law, that we might receive the adoption as sons.
⁶  And because you are sons, God has sent forth the Spirit of his Son into your hearts, crying out, “Abba, father!”
⁷  Therefore you are no longer a slave but a son, and if a son, then an heir of God through Christ.
⁸  But then, indeed, when you did not know God, you served those which by nature are not gods.
⁹  But now after you have known God, or rather are known by God, how is it that you turn again to the weak and beggarly elements, to which you desire again to be in bondage?

    We thus become a different being than anything anyone in the Old Covenant had ever seen or experienced. Being born of God is something the world and its beggarly elements under the Law could not ever produce. The final result [end] of life in the spirit is what the Old Covenant Jews were prevented from gazing into when Moses covered his face with a veil. His face anticipated the glorious spiritual life that was coming to all who came to Christ by letting the Law be their tutor. This divine life is what we are changed into by gazing into the glorious face of Jesus Christ.

Conclusion:
     I think it is amazing how much of the sayings of Jesus open up to our understanding when we have two key elements in mind as we read.

    1.) That Jesus had come to give Spiritual Life to the Jews, something that they did not, nor did their fathers ever have the privilege of receiving -- they could only embrace the promises and wait for the fulfillment. The fulfillment came and the majority of Israel rejected the prize, as their covenant, place and nation came to a close.

    2.) That he was returning shortly to the earth with his kingdom in the glory of his father and all his holy angels and would then judge them and destroy their city and nation, and then open up the kingdom to the world.

    Looking back now at the end of the age, ("Remembering the End of the World"), we on the other side of history can now say that God has begun a life in us. It is a holy life. It is the very life of Life himself, Jesus Christ. God wants us to enjoy it to the fullest and one day be revealed in glory with unimaginable joy in his presence forever.
    That expectation can be yours, if you will come to him to have life. By faith, placing your life in his hands, changing your mind about your actions, (repentance) and be immersed in water for the forgiveness of your sins - his life can be yours today.

(Originally delivered in Onondaga, WA,  August, 23, 2009)