Thomas Aquinas, on Ps 50:17

“O Lord, thou wilt open my lips: and my mouth shall declare thy praise.”

“Hence he adds, "A sacrifice to God," namely one that is acceptable, "is a contrite spirit." Augustine, in City of God 10: Every sacrifice that is offered externally is a sign of an interior sacrifice, in which one offers one's soul to God. But it should be known that the soul of a person is led into sin first through vain joy. Eccl. 2: "Laughter I considered an error, and to joy I said: Why are you vainly deceived?" that is, led into sin. Second, it is hardened against spiritual things through sin. Sir. 3: "A hard heart shall fare ill at the last." Rom. 2: "According to your hardness and impenitent heart." Third, because it is self-sufficient in bodily things and does not care about spiritual things, then it becomes proud, which is the beginning of all sin, Sir. 10. It is necessary, therefore, that the penitent who offers his heart as a sacrifice to God do the opposite of all these things. And first, against vain joy, he must take on the sorrow of penance; and therefore he adds, "A sacrifice to God is a contrite spirit," that is, one who is sorrowful about all his sins together, not just about one. 2 Cor. 7: "The sorrow that is according to God works repentance unto steadfast salvation." Bar. 2: "The soul that is sorrowful over the greatness of evil and walks bowed down." And below: "gives you glory and sorrow to the Lord." Against the second is opposed contrition; hence he says, "a contrite heart." And note the difference between "broken" and "contrite": for "broken" things are divided into large parts; "contrite" things are divided into very small parts. Therefore, as long as someone has a hard heart, his heart is, as it were, intact in malice; but when he totally abandons sin, giving himself over to spiritual things, then he is said to be contrite. Job 16: "I, once prosperous" -- namely in temporal things -- "was suddenly crushed." Against the third is opposed humility; and therefore he says, "and a humbled heart, O God, you will not despise," because God resists the proud but gives grace to the humble, Jas. 4. And it should be known that he mentions heart and spirit, and spirit pertains to courage, and thus pertains to the irascible power. Is. 25: "The spirit of the strong, like a whirlwind driving against a wall." Heart pertains to the concupiscible power; and so through this it is given to understand that whatever is in the appetitive power must be offered to God in sacrifice.”

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