And all flesh died that moved upon the earth, both of fowl, and of cattle, and of beast, and of every creeping thing that creepeth upon the earth, and every man:

Wesley's Notes

7:21 All flesh died, all in whose nostrils was the breath of life, of all that was on the dry land, every living substance - And why so? Man only had done wickedly, and justly is God's hand against him, but these sheep what have they done? I answer,
1. We are sure God did them no wrong. He is the sovereign Lord of all life, for he is the sole fountain and author of it. He that made them as he pleased, might unmake them when he pleased, and who shall say unto him, What dost thou?
2. God did admirably serve the purposes of his own glory by their destruction, as well as by their creation. Herein his holiness and justice were greatly magnified: by this it appears that he hates sin, and is highly displeased with sinners, when even the inferior creatures, because they are the servants of man, and part of his possession, and because they have been abused to be the servants of sin, are destroyed with him. It was likewise an instance of God's wisdom. As the creatures were made for man when he was made, so they were multiplied for him when he was multiplied; and therefore, now mankind was reduced to so small a number, it was fit that the beasts should proportionable be reduced, otherwise they would have had the dominion, and would have replenished the earth, and the remnant of mankind that was left would have been overpowered by them.

Jamieson-Fausset-Brown Bible Commentary

21. all flesh died . fowl . cattle, and . creeping thing-It has been a uniform principle in the divine procedure, when judgments were abroad on the earth, to include every thing connected with the sinful objects of His wrath (Ge 19:25; Ex 9:6). Besides, now that the human race was reduced to one single family, it was necessary that the beasts should be proportionally diminished, otherwise by their numbers they would have acquired the ascendancy and overmastered the few that were to repeople the world. Thus goodness was mingled with severity; the Lord exercises judgment in wisdom and in wrath remembers mercy.

Matthew Henry's Concise Commentary

7:21-24 All the men, women, and children, that were in the world, excepting those in the ark, died. We may easily imagine what terror seized them. Our Saviour tells us, that till the very day that the flood came, they were eating and drinking, Lu 17:26,27; they were deaf and blind to all Divine warnings. In this posture death surprised them. They were convinced of their folly when it was too late. We may suppose they tried all ways and means possible to save themselves, but all in vain. And those that are not found in Christ, the Ark, are certainly undone, undone for ever. Let us pause, and consider this tremendous judgment! Who can stand before the Lord when he is angry? The sin of sinners will be their ruin, first or last, if not repented of. The righteous God knows how to bring ruin upon the world of the ungodly, 2Pe 2:5. How tremendous will be the day of judgment and perdition of ungodly men! Happy they who are part of Christ's family, and safe with him as such; they may look forward without dismay, and rejoice that they shall triumph, when fire shall burn up the earth, and all that therein is. We are apt to suppose some favourable distinctions in our own case or character; but if we neglect, refuse, or abuse the salvation of Christ, we shall, notwithstanding such fancied advantages, be destroyed in the common ruin of an unbelieving world.