Development of Afterlife Doctrine

This is a difficult question to answer because it pertains to what the people believed and at what time they believed it. It is much easier to say what the Bible teaches and what the people should have believed!

Certainly by the time of the New Testament many Israelites believed in a resurrection unto eternal life. The resurrection was affirmed by the Pharisees, but denied by the Sadducees (Acts 23:6-8). Of course, the resurrection unto eternal life was taught in the Old Testament, which is why the Pharisees affirmed it.

Jesus himself argued with the Sadducees on this point, teaching that the resurrection is proven by the fact that the Old Testament refers to the dead as still serving God (Matt. 22:23-32). In Matthew 22:32, Jesus based this argument on Exodus 3:6. (He did this because the Sadducees recognized the authority of the books of Moses, but rejected most others.) So, according to Jesus, at least Moses believed in an afterlife. Whether or not Moses' followers also believed it, they should have believed it based on Moses' teachings.

To go back a bit farther, we find Abraham's faith that God could restore Isaac from the dead (Gen. 22 w/ Heb. 11:17-19), which would seem to imply that Abraham believed Isaac still existed somewhere after death. And even before this, we have the biblical example of the primeval father Enoch in Genesis 5:24, who was taken into heaven (Heb. 11:5).

Even at the very beginning, Moses recorded that Abel's blood cried to God from the ground. This may not look like a direct reference to an afterlife, but I think it is. We find such confirmation of this idea in Hebrews 11:4, where the author says that Abel still speaks. Also, Revelation 6:9-10 suggests the way that Abel's blood cried out to God when it describes the petitions of the slain saints in heaven.

Besides these, Job expressed a belief in a physical afterlife (Job 19:25) as well as a belief in the existence of departed spirits (Job 26:5). Isaiah 14:9; 26:14-19 and Psalm 88:10 also speak of departed spirits. Many other passages suggest similar ideas.

So, it seems to me that biblical books from a wide range of ages — from the oldest on down — speak of an afterlife. And the Mosaic texts suggest that the ideas as old as mankind. A number of texts also speak of a resurrection from the dead, and many more imply it. At least some people in Israel and Judah, then, actually believed in these things, and all of them should have believed in them. How many actually did believe them? It's hard to say before the time of the Pharisees.