Genesis 6:17 - Matthew Poole's English Annotations on the Holy Bible

I, even I, which is thus emphatically repeated, to signify that this flood did not proceed from natural causes, but from the immediate hand and judgment of God, do bring, i.e. will assuredly and speedily bring, all flesh, i.e. all men, birds, and beasts. Every thing that is in the earth. This limitation is added to show, that the fishes are not included in the threatened destruction, either because they did not live in the same element wherein men lived and sinned; or because they were not so instrumental in men's sins as the beasts might be; or because man had a greater command over the beasts than over the fishes, and greater service and benefit from them; and therefore the destruction of the former was a greater and more proper punishment to man than the latter.