John Calvin Commentary Psalms 139:21

"Do not I hate them, O Jehovah, that hate thee? And am not I grieved with those that rise up against thee?" — Psalms 139:21 (ASV)

Shall I not hold in hatred those that hate thee? He proceeds to mention how greatly he had profited from the meditation on God into which he had been led. For, as the effect of his having realized his presence before God’s bar, and reflected upon the impossibility of escaping the eye of him who searches all deep places, he now lays down his resolution to lead a holy and pious life.

In declaring his hatred of those who despised God, he virtually asserts by this his own integrity—not as being free from all sin, but as being devoted to godliness, so that he detested in his heart everything that was contrary to it.

Our attachment to godliness must be inwardly defective if it does not generate an abhorrence of sin, such as David here speaks of. If that zeal for the house of the Lord, which he mentions elsewhere (Psalms 69:9), burns in our hearts, it would be an unpardonable indifference to look on silently when his righteous law is violated, indeed, when his holy name is trampled upon by the wicked.

Regarding the last word in the verse, קוט, kut, means to dispute with, or contend, and may be understood as retaining the same sense here in the Hithpael conjugation, unless we consider David to have meant more particularly that he inflamed himself, stirring up his mind to contend with them.

We thus see that he stood forward strenuously in defense of the glory of God, regardless of the hatred of the whole world, and waged war with all the workers of iniquity.