Why does the Jewish bible (Torah) repeat itself, especially in Genesis?
The documentary hypothesis states that different parts of the Torah were written by different people–E (for Elohim), J (for “YHVH”), P (for priestly) and D (for deuteronomic). In some cases the same part is found in two or more of these original writers’ versions, and when the final version of the Torah was redacted, probably by Ezra, they were combined since (presumably) these texts were so well-known that to leave out parts of any of them would have been problematic. On the other hand, all of these duplications have been very nicely explained by Talmudic-era rabbis as being there to teach us something. Take your pick.
