Matthew Poole and continuators on Deuteronomy 32:42

42 I will make mine arrows drunk with blood (and my sword shall devour flesh) and that with the blood of the slain, and of the captives , from the beginning of revenges upon the enemy .

Whom my sword hath sorely wounded, though not utterly killed.

(i. e.) When once I begin to revenge my self and my people upon mine and their enemies, I will go on and make a full end. Or, with the head, or with the blood of the bead, i. e. of the chief or chiefs, of the revenges of the enemy, i. e. of the revengeful or malicious enemy of God and of his people. The noun substantive is oft put for the adjective, as Gen. 17. 5. a multitude of nations is put for many nations, Rom. 4. 17. and Gen. 45. 22. changes of raiment, i. e. changeable raiment; and Psal. 99. 4. the kings strength, i. e. the strong and mighty king. And so here, the revenges of the enemy, i. e. the revengeful enemy. And by the head may be here understood either the Devil, or the heads and rulers of those Empires which were enemies to Gods people. Or, of the head shall be the revenges upon the enemies, i. e. I will take vengeance upon all mine enemies, yea upon the head or heads of them.

Marginal references: Job 13. 24 Jer. 30. 14 Lam. 2. 5.