7:1 have I seen righteous. This is the first mention of the doctrine of justification in the Bible–that is, of being “seen as righteous” by God. The same word is translated “just” in Genesis 6:9 (“Noah was a just man”). The reason why Noah could be seen as “justified” was that he had “found grace in the eyes of the LORD” (Genesis 6:8). Also, see note on Genesis 15:6.
7:2 by sevens. The “clean” kinds of beasts and birds were those suitable for domestication and a form of fellowship with man, as well as for sacrificial offerings. Apparently three pairs of each of these were preserved in order to allow for wider variation in breeding after the Flood. The seventh was offered by Noah in sacrifice when they left the ark (Genesis 8:20).
7:3 keep seed alive. God’s purpose for the ark was to “keep seed alive” in the earth, a statement meaningful only in the context of a universal flood. The ark was far too large to accommodate merely a local or regional fauna. In fact, if the Flood were only local, the ark would not have been needed at all. Noah’s family, as well as the birds and beasts, could far more easily have simply migrated away from the region to be flooded.
7:4 seven days. This seven-day period of final warning and preparation marks the first of many references to seven-day intervals during the Flood year. This fact makes it obvious that the practice of measuring time in seven-day weeks had been in effect throughout the period between the creation week and the Flood.
7:4 forty days. A worldwide rain lasting forty days would be impossible under present meteorologic conditions. The condensation of the antediluvian vapor canopy, the “waters above the firmament” (Genesis 1:6-8) is the only adequate explanation.