Adam Clarke on Deuteronomy 32:27

Were it not that I feared the wrath of the enemy - Houbigant and others contend that wrath here refers not to the enemy, but to God; and that the passage should be thus translated: "Indignation for the adversary deters me, lest their enemies should be alienated, and say, The strength of our hands, and not of the Lord's, hath done this." Had not God punished them in such a way as proved that his hand and not the hand of man had done it, the heathens would have boasted of their prowess, and Jehovah would have been blasphemed, as not being able to protect his worshippers, or to punish their infidelities. Titus, when he took Jerusalem, was so struck with the strength of the place, that he acknowledged that if God had not delivered it into his hands, the Roman armies never could have taken it.