Western Saints
Augustine of Hippo
"For the Lord knoweth the way of the righteous" (ver. 6). As it is said, medicine knows health, but knows not disease, and yet disease is recognised by the art of medicine. In like manner can it be said that "the Lord knoweth the way of the righteous," but the way of the ungodly He knoweth not. Not that the Lord is ignorant of anything, and yet He says to sinners, "I never knew you." "But the way of the ungodly shall perish;" is the same as if it were said, the way of the ungodly the Lord knoweth not. …
On the Psalms, Psalm 1 ↗
Ambrose of Milan
It follows: For the Lord knows the way of the righteous, and the way of the wicked shall perish. Pay attention to the meaning: The wicked do not rise in judgment, for the Lord knows the way of the righteous. Certainly He knows their ways, whose steps are directed by the Lord. They are the steps of men who are guided by the Lord. They are guided by the Lord and the ways of man. The Lord knows these ways, which are straight and tend toward that life of which it is said: I am the way, the truth, and the life (John 14:6). …
Commentaries on the Twelve Davidic Psalms ↗
Jerome
For the Lord knows the way of the just, and the way of the ungodly shall perish. For the Lord knows the way of the just. And what is so great, if the Lord knows the way of the just? But God is said to know those whom he deigns to know. Indeed it is said of sinners: 'Depart from me, workers of iniquity, I do not know you.' The apostle says: 'If anyone knows, he is known.' For the Lord knows the way of the just. He who is a sinner, the Lord does not know him; he who is just, is known by God. …
Homily 1, on Psalm 1 ↗