When we read the end of Bereshit followed by the beginning of Noach, we notice that God gets upset twice, and twice makes a decree to destroy humanity, with the exception of Noach and his family. The first time is in Bereshit 6:5-8 (at the end of Bereshit) and then again in 6:11-18 (at the beginning of Noach). Why is there this repetition?
Rabbi Mordechai Breuer addresses this issue in chapter 8 of his book, Pirkei Bereshit. (I also heard him give a lecture on it in Yeshivat HaKibbutz HaDati in the early 1990s.) He points out that both verse 5 and verse 12 start with the word vayar (“[He] saw”). But significantly, verse 5 uses the name YKVK, whereas verse 12 uses the name Elokim. These names represent two aspects of God. The former represents the divine attribute of mercy – midat harachamim, and the second the divine attribute of justice – midat hadin. And in this case neither aspect could prevent the flood. He then goes on to show that there is a double narrative throughout the Flood story. Aside from what I’ve already mentioned, Noach twice receives instructions about the ark and the animals (6:14-22 and 7:1-5). And then Noach and his family enter the ark twice (7:7-9 and 7:13-16) while everyone left on earth dies (7:21 and 7:23), and more. There are differences between each story (the number of days before the flood for the survivors to board the ark, how many animals – 2 or 7 – of each kind to take, and how long the flood actually lasted).
The commentaries try to resolve the difficulties by finding harmony between all the verses. Rabbi Breuer says the better option is to understand each story separately, according to the attribute of God that appears in it. Just as there are two stories of the creation of the world (Bereshit 1 and Bereshit 2), each according to a different aspect of God, so too are there two stories of the destruction of the world.
I won’t go into all the details here about how he explains the flood story (and the “recreation” story following it) Much of it has to do with whether humanity is distinct from the animal kingdom (as in 6:5 – “how great was man’s wickedness on earth”) or whether animals and humans share the same realm (as in 6:12 – “God saw how corrupt the earth was, for all flesh had corrupted its ways on earth”).
But I do think that the break between the end of Bereshit and the beginning of Noach was deliberate, to avoid over-emphasizing the repetitiveness, and allowing for a more fluid reading of the two interlocked stories.