John Gill Commentary Deuteronomy 12:20

"When Jehovah thy God shall enlarge thy border, as he hath promised thee, and thou shalt say, I will eat flesh, because thy soul desireth to eat flesh; thou mayest eat flesh, after all the desire of thy soul." — Deuteronomy 12:20 (ASV)

When the Lord your God shall enlarge your border, as he has
promised you
Brought them into the land of Canaan, where they should have large and good pastures for the feeding of their cattle, which they had not in the wilderness, and so a greater increase of them:

and you shall say, I will eat flesh ;
which they were shorts of, or ate but little of in the wilderness, lest their herds and their flocks should be consumed; but now having room to feed them, and an increase of them, they would give themselves a greater liberty of eating flesh:

because your soul longeth to eat flesh ;
would have a craving appetite unto it, having so long ate none, or very little:

you may eat flesh, whatsoever your soul lusteth after ;
of any sort that is clean, and allowed to be eaten, and as much of it as is craved, only intemperance must be guarded against.