John Calvin Commentary Deuteronomy 33:20

"And of Gad he said, Blessed be he that enlargeth Gad: He dwelleth as a lioness, And teareth the arm, yea, the crown of the head." — Deuteronomy 33:20 (ASV)

And of Gad he said. In the blessing of the tribe of Gad, mention is made only of the hereditary portion, which it had obtained without casting lots. He therefore celebrates the blessing of God, because He had granted to the Gadites an ample dwelling place; for the word “enlargeth” refers to the extent of their possession.

But since, in that farthest part of the land beyond the Jordan, they were on a hostile border, he declares that they would be warlike, and thus compares them to a lion, which tears its prey sometimes from the head and sometimes from the arm. Since, then, that position would not be as peaceful as any other region in the midst of Canaan, he declares that they would be safe and sound through their own boldness.

And although it is not a very pleasant condition to be harassed by constant wars, still, in such an unpleasant situation, God’s grace should not be despised, which made them formidable to their enemies and of great valor, by which they might not only repel hostile invasions but also be willing on their own to undertake predatory expeditions.

If anyone objects that a license for plunder was entirely unsuitable for God’s children, the solution is obvious: reference is not made here to what was lawful, or what was desirable and praiseworthy, but a consolation was offered to them as protection against the incursions and annoyances of their enemies. Besides, the lust for booty is not permitted, but praise is given merely to their courage in overcoming their enemies.