I've enjoyed reading through the majority of your answers very much. It's nice to see such a straight-forward answering all types of questions.
Forgive me if you've answered this before, but I'm trying to determine when the concept of eternal life in heaven or hell first occurred in the Bible. Unless I'm mistaken, most (if not all) of the major Old Testament figures (Abraham, Moses, etc.) don't seem to have that understanding. I understand the differences in the Old and New Covenants, but to the best of my understanding the saved of our time will be joined in heaven by the saved from the older dispensations. I take the parable of the afterlife discussion between the rich man and Abraham as an example of this principle.
So, when did this understanding begin?
People have a tendency to make assumptions when no information is present. Thus, you find people assuming because information about early life on earth wasn't well preserved that mankind must have lived primitively in caves. It used to be argued that Moses couldn't have written the first five books of the Old Testament because we had no evidence that people knew how to write that long ago -- we've since found out that writing was quite common, thank you very much. Or that the Hittite nation couldn't have existed as stated in the Bible because we had no confirmation that there was a Hittite nation -- we've found that since then as well.
Pay very close attention when conclusions are drawn on a lack of information. A lack of information actually tells us that we don't know and no conclusion can be drawn. Just because I don't find Abraham talking about eternal life, can I rightly draw the conclusion that he didn't have knowledge of it? Actually the writer of Hebrews suggests otherwise:
"By faith Abraham obeyed when he was called to go out to the place which he would receive as an inheritance. And he went out, not knowing where he was going. By faith he dwelt in the land of promise as in a foreign country, dwelling in tents with Isaac and Jacob, the heirs with him of the same promise; for he waited for the city which has foundations, whose builder and maker is God. 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. 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. 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. For those who say such things declare plainly that they seek a homeland. And truly if they had called to mind that country from which they had come out, they would have had opportunity to return. 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" (Hebrews 11:8-16).
From various hints in the book of Job, we are fairly sure Job lived not too long after the flood, perhaps as a contemporary of Abraham. Job and his friends in their arguments show a sophisticated understanding of morality and the nature of God that goes against the grain of modern history. Today people think we evolve from primitive thinking to greater ideas. The Bible suggests the opposite. Man tends to decay and to forget the things he once knew unless actively reminded. "Is there anything of which it may be said, "See, this is new"? It has already been in ancient times before us. There is no remembrance of former things, Nor will there be any remembrance of things that are to come By those who will come after" (Ecclesiastes 1:10-11).
Job says some things about the afterlife that ought to make you sit up and take notice because it is found in such an old book. For instance, Job understood that a person only lives once:
"For there is hope for a tree, if it is cut down, that it will sprout again, and that its tender shoots will not cease. Though its root may grow old in the earth, and its stump may die in the ground, yet at the scent of water it will bud and bring forth branches like a plant. But man dies and is laid away; indeed he breathes his last and where is he? As water disappears from the sea, and a river becomes parched and dries up, so man lies down and does not rise. Till the heavens are no more, they will not awake nor be roused from their sleep" (Job 14:7-12).
Though he speaks of the finality of death, yet he also doesn't see death as permanent. He calls it "sleep" from which a person eventually awakens.
Job refers to Sheol, the Hebrew word for the grave. Not the physical grave but the realm of the dead where people go when they die.
"Oh, that You would hide me in the grave, that You would conceal me until Your wrath is past, that You would appoint me a set time, and remember me!" (Job 14:13).
Job also knew that when people did arise from the grave that they would have new bodies.
"If a man dies, shall he live again? All the days of my hard service I will wait, till my change comes" (Job 14:14).
In case that reference to his "change" isn't clear, Paul talked of the same thing.
"So also is the resurrection of the dead. The body is sown in corruption, it is raised in incorruption. It is sown in dishonor, it is raised in glory. It is sown in weakness, it is raised in power. It is sown a natural body, it is raised a spiritual body. There is a natural body, and there is a spiritual body. ... Behold, I tell you a mystery: We shall not all sleep, but we shall all be changed -- in a moment, in the twinkling of an eye, at the last trumpet. For the trumpet will sound, and the dead will be raised incorruptible, and we shall be changed" (I Corinthians 15:42-44, 51-52).
But beyond all of that, Job knew about life after death.
"For I know that my Redeemer lives, and He shall stand at last on the earth; and after my skin is destroyed, this I know, that in my flesh I shall see God, whom I shall see for myself, and my eyes shall behold, and not another. How my heart yearns within me!" (Job 19:25-27).
Job is saying that he knows that at that very moment his redeemer lives and will one day physically stand on this earth, but it will be long after Job has died and his body had crumbled away. Yet Job also knew that he would get to actually see this Redeemer, his God, directly for himself! In other words, Job knew that the Son of God was coming one day to the earth and that after the resurrection Job would, in his new body, be able to see his Savior in heaven.
Job's concept of death, resurrection, life after death and resurrection is much more accurate than most people have today.
That death wasn't the final end is hinted at in Genesis. When the patriarchs died, it was spoken of as joining those who already died.
"Then Abraham breathed his last and died in a good old age, an old man and full of years, and was gathered to his people" (Genesis 25:8).
"So Isaac breathed his last and died, and was gathered to his people, being old and full of days. And his sons Esau and Jacob buried him" (Genesis 35:29).
"And when Jacob had finished commanding his sons, he drew his feet up into the bed and breathed his last, and was gathered to his people" (Genesis 49:33).
Notice that in Isaac's case, Isaac was gathered to his people before his sons buried him. The phrase indicates the knowledge that those who died before are still living, just not in this world.
Jesus proved that there was life after death by quoting from an event that happened to Moses. "Moreover He said, "I am the God of your father-the God of Abraham, the God of Isaac, and the God of Jacob." And Moses hid his face, for he was afraid to look upon God" (Exodus 3:6). Jesus pointed out that God said, "I am" and not "I was." Therefore, the implication is that Abraham, Isaac, and Jacob still lived. Using that as a hint, we find God telling Isaac after his father's death, "I am the God of your father Abraham; do not fear, for I am with you. I will bless you and multiply your descendants for My servant Abraham's sake" (Genesis 26:24). Thus from early times, men knew that people lived after death.
When David's infant son died, he made this interesting observation, "But now he is dead; why should I fast? Can I bring him back again? I shall go to him, but he shall not return to me" (I Samuel 12:23).
As far as eternal life being possible, it was first mentioned in Genesis 3:22, "Then the LORD God said, 'Behold, the man has become like one of Us, to know good and evil. And now, lest he put out his hand and take also of the tree of life, and eat, and live forever.'" That eternal life is available for the righteous was stated by Solomon, "The fruit of the righteous is a tree of life, and he who wins souls is wise" (Proverbs 11:30). David also hint at life, but used the image of water, "For with You is the fountain of life; in Your light we see light" (Psalm 36:14). And at the end of David's famous Psalm, he expressed the desire for God to care for him in this life and to dwell with God forever. "Surely goodness and mercy shall follow me all the days of my life; and I will dwell in the house of the LORD forever" (Psalm 23:6).
Similarly, there is mention of eternal destruction. "The sinners in Zion are afraid; Fearfulness has seized the hypocrites: 'Who among us shall dwell with the devouring fire? Who among us shall dwell with everlasting burnings?'" (Isaiah 33:14). In stark contrast to the death of his infant, when David's son Absalom died, there was no mention of seeing him after death. "O my son Absalom-my son, my son Absalom - if only I had died in your place! O Absalom my son, my son!" (II Samuel 18:33). David had no fear of personally dying, but he did not hold hope for Absalom after his death.
Like the concept of God, angels, and other matters we don't find a development of a theme, but an assumption that people knew these things existed. We gather clues about their knowledge of these things from various comments which are recorded for us, but there is no detailed explanation of these things. Not until we get to the New Testament is the fullness of what was only hinted at discussed at length. "Of this salvation the prophets have inquired and searched carefully, who prophesied of the grace that would come to you, searching what, or what manner of time, the Spirit of Christ who was in them was indicating when He testified beforehand the sufferings of Christ and the glories that would follow. To them it was revealed that, not to themselves, but to us they were ministering the things which now have been reported to you through those who have preached the gospel to you by the Holy Spirit sent from heaven--things which angels desire to look into" (I Peter 1:10-12).
Yes, salvation does come to the ancients as well as us. Jesus died for both the people in the past as well as those in the future. "And for this reason He is the Mediator of the new covenant, by means of death, for the redemption of the transgressions under the first covenant, that those who are called may receive the promise of the eternal inheritance" (Hebrews 9:15).