Augustine of Hippo

"Forsake me not, O Lord; O my God, depart not from me" [Psalm 38:21]. Let us speak in Him, let us speak through Him (for He Himself intercedes for us), and let us say, "Forsake me not, O Lord my God." And yet He had said, "My God! My God! Why have You forsaken Me?" [Matthew 27:46] and He now says, "O My God, depart not from Me." If He does not forsake the body, did He forsake the Head? Whose words then are these but the First Man's? …

Exposition on Psalm 38 ↗

Ambrose of Milan

And yet, although he follows righteousness, he does not consider it to be of his own virtue, but of heavenly grace, if he is not forsaken by Christ; and for this reason he prays more earnestly, saying: Do not forsake me, O Lord my God; do not depart from me; that is, men have forsaken me, my friends have attacked the one who is dear to them: they have not drawn near. …

Commentaries on the Twelve Davidic Psalms ↗

Thomas Aquinas

"Do not forsake me, O Lord." Here is set forth the prayer; and he asks that what he fears be removed, and he asks that what he loves be given to him, at "Attend to my help." Here he asks that what he fears not be removed, namely the presence of God; hence he says, "Do not forsake me, O Lord my God," namely in tribulation. Ps. 90: "I am with him in tribulation." Dt. …

Exposition on the Psalms of David ↗