Thomas Aquinas, on Ps 16:1

“The prayer of David. Hear, O Lord, my justice: attend to my supplication. Give ear unto my prayer, which proceedeth not from deceitful lips.”

“Above, the Psalmist described divine justice and showed that he observed it; here he sets forth a prayer in which he asks to be heard on account of his justice. The title is "A prayer of David." And it is the first Psalm that is titled from prayer, because it is entirely a prayer; and therefore it begins with prayer, because among tribulations the singular refuge is prayer. Ps. 108: "In return for my love, they slandered me; but I prayed." This Psalm is therefore divided into two parts. In the first, he prays for his own stability; in the second, he asks for deliverance from evil, at "I cried out." Concerning the first, he does two things. First, he asks to be heard; second, he sets forth his petition, at "From your countenance." It should be considered, moreover, that in the hearing of prayer there is a threefold degree. First, the one to whom the petition is made hears the words. Second, he attends to the meaning. Third, he fulfills what is asked. First, therefore, he asks to be heard, saying, "Hear," etc. Dan. 9: "Hear, O Lord God, the prayer of your servant." Second, in the hearing he sets forth the merit of the petitioner; and therefore he says, "my justice"; as if to say: in me there is merit that you should hear me. The Gloss says: Justice has a voice before God, by which it penetrates heaven. Jas., last chapter: "The persistent prayer of a just man avails much." Jn. 9: "God does not hear sinners; but if anyone is a worshiper of God, God hears him." Second, he asks that God attend to the meaning of the prayer: "attend to my supplication." The Gloss says: "supplication," which is for the removal of evils. Another reading has, "attend to my songs," as if to the spiritual meaning. Ps. 129: "Let your ears be attentive to the voice of my supplication." Third, that he hear the words of the one praying; and therefore he says, "Give ear to my prayer, which is not on deceitful lips," but on simple ones. Is. 53: "Deceit was not in his mouth." But since God hears all things, why is he said to hear some things and not others? Wis. 1: "The Holy Spirit of discipline will flee from the deceitful and will withdraw from thoughts that are without understanding." God is not said to hear except true words, and not those that come from deceitful lips; and therefore he says, "not on deceitful lips." Ps. 11: "Deceitful lips, from a double heart," etc. And thus "deceitful" is taken in two ways: namely, pretense with respect to the mouth, and with respect to deeds, when the deed does not agree with the mouth. The Pharisee who said (Lk. 18), "I am not like the rest of men," etc., was not heard; but the other, who prayed not on deceitful lips but rightly, was heard, because "he went down to his house justified." The Gloss says: Deceitful lips are those who say "Lord, Lord" and do not do the will of my Father.”

Imported from an open dataset — not yet checked against the printed edition.