Where is the concept of Heaven or Hell first introduced in the Bible? I assume it would be somewhere in Genesis after the fall when death is first introduced. Would Adam and Eve have known how believing in God was the means to spending eternity with Him?
The first reference to death and the way of eternal life is found in Genesis 3:
The Lord alludes to living forever as He references the tree of life. Later, God revealed more and more details of life after death to mankind progressively over centuries of time, but that process isn't necessarily recorded in Scripture. For example, Abel and Cain knew to sacrifice to God as seen in Genesis 4, but the moment they learned this requirement isn't recorded in Scripture. More than likely, they learned it from their parents, who experienced the first sacrificial act in Genesis 3:21.