John Calvin Commentary Genesis 7:2

"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:" — Genesis 7:2 (ASV)

Of every clean beast. He again repeats what he had previously said concerning animals, and not without reason. For there was considerable difficulty in collecting from woods, mountains, and caves such a great multitude of wild beasts, many species of which were perhaps entirely unknown; and in most of them, there was the same ferocity that we now perceive.

Therefore, God encourages the holy man, lest, being alarmed by that difficulty and having cast aside all hope of success, he should fail. Here, however, at first sight, some kind of contradiction appears, because while he had previously spoken of pairs of animals, he now speaks of sevens. But the solution is close at hand: previously, Moses did not state the number but only said that females were added as companions to the males, as if he had said that Noah himself was commanded not to gather the animals indiscriminately, but to select pairs from them for the propagation of offspring. Now, however, the discussion concerns the actual number.

Moreover, the expression "by sevens" is to be understood not as seven pairs of each kind, but as three pairs, to which one animal is added for sacrifice. Besides, the Lord intended that a threefold greater number of clean animals than of others be preserved, because they would be more necessary for human use. In this provision, we must consider the fatherly goodness of God toward us, by which He is inclined to care for us in all things.