See Chapter 8:1-10. At the end of forty days (from the time the ark came to rest) Noach first sent the raven (which returned) and then the dove (which also returned). Noach waited seven more days before he once again sent the dove.
This is the reverse of what had transpired at the onset of the Mabul. Noach is told that he should enter the ark with all the animals because in another seven days there will be a flood for forty days. (7:4)
We are taught (ב”ר לב, ה) that the forty days of the flood allude to the forty days needed for the formation of the human fetus. These forty days were the time period of the formation of a new world. (From commentary on 7:4).
When the ark came to rest, Noach waited forty days (apparently for another time period of formation – GS). He sent the raven, and the dove but they both returned. He then continued to wait. He chose to wait seven more days, the mirror image of the seven days prior to the flood.
The significance of seven days is a transition period. We will encounter a similar ideas behind seven days with the laws of טומאה וטהרה – (such as in the laws of נדה and the laws of מצורע. ) A seven day period marks the complete cessation of one state, before the onset of a new state.
Beraishis 8:1-10
pages 200-204
