the flesh of kings, the flesh of captains, the flesh of mighty men . . . free and slave, both small and great
Captains is χιλιάρχων [chiliarchōn] : leaders over a thousand troops. The same word is translated commanders in Revelation Rev. 6:15+. These same categories of men previously hid in caves from Gods wrath (Rev. Rev. 6:15-17+). See commentary on Revelation 6:15.
Normally, men are to offer up animals in sacrifice to God. Here, as when God judges Gog on the mountains of Israel, He reverses the normal roles and offers up men as a sacrifice to animals (Eze. Eze. 39:17-20 cf. Isa. Isa. 34:6-7).
Goliath threatened David, Come to me, and I will give your flesh to the birds of the air and the beasts of the field! (1S. 1S. 17:44). David replied, This day I will give the carcasses of the camp of the Philistines to the birds of the air and the wild beasts of the earth, that all the earth may know that there is a God in Israel (1S. 1S. 17:46).
The repetition of the word flesh, occurring five times over, flesh, flesh, is very revealing. The race has walked in carnal enmity against God, living after the flesh, and now the day of His patience is at an end.1