John Calvin Commentary 1 Corinthians 15:39

"All flesh is not the same flesh: but there is one [flesh] of men, and another flesh of beasts, and another flesh of birds, and another of fishes." — 1 Corinthians 15:39 (ASV)

All flesh is not, etc. Here we have another comparison leading to the same conclusion, though there are some who explain it otherwise. For when he says that under the term flesh is included the body of a man as well as of a beast, and yet the flesh in those two cases is different, he means by this that the substance indeed is the same, but there is a difference in quality. The sum is this—that whatever diversity we see in any particular kind is a sort of prelude to the resurrection, because God clearly shows that it is not difficult for him to renew our bodies by changing the present condition of things.