Charles Spurgeon Commentary Genesis 7:2-3

"Of every clean beast thou shalt take to thee seven and seven, the male and his female; and of the beasts that are not clean two, the male and his female: of the birds also of the heavens, seven and seven, male and female, to keep seed alive upon the face of all the earth." — Genesis 7:2-3 (ASV)

Of the clean creatures that could be offered in sacrifice to God, you see that there was a larger proportion of them than of the unclean, so that there might be sufficient for sacrifice without the destruction of any species. The unclean beasts were mostly killers and devourers of others, and therefore their number was to be less than that of the clean species. Oh, that the day might soon come when there would be more clean men and women than unclean ones, when there would be fewer sinners than godly people in the world, though even then there would be the ungodly "by two" like the unclean beasts.