Adam Clarke on Ezekiel 35:5

A perpetual hatred - The Edomites were the descendants of Esau; the Israelites, the descendants of Jacob. Both these were brothers; and between them there was contention even in the womb, and they lived generally in a state of enmity. Their descendants kept up the ancient feud: but the Edomites were implacable; they had not only a rooted but perpetual enmity to the Israelites, harassing and distressing them by all possible means; and they seized the opportunity, when the Israelites were most harassed by other enemies, to make inroads upon them, and cut them off wherever they found them.

To afflict the afflicted is cruel. This is scarcely of man, bad as he is. He must be possessed by the malignant spirit of the devil, when he wounds the wounded, insults over the miseries of the afflicted, and seeks opportunities to add affliction to those who are already under the rod of God.