Thomas Aquinas, on Ps 49:18

“If thou didst see a thief thou didst run with him: and with adulterers thou hast been a partaker.”

“"If you saw a thief, you ran with him." Here he sets forth the malice of sinners with respect to the commission of evil. But a little earlier he showed their defect with respect to the desertion of good, when he said, "But you have hated," etc. And first he sets forth their wickedness with respect to evil works; then with respect to evil words. He says, therefore, "If you saw." Where it should be known that these words are proposed in the person of God to the sinner who announces and preaches the justice of God. And they are especially suited to prelates and teachers, who do not easily fall into sin themselves, but consent to others who sin, and these things are turned against them. Rom. 1: "Not only those who do these things are worthy of death, but also those who consent," etc. 1 Sam. 2: "Eli was punished because he did not correct his sons." Therefore he reproves them for this. And he touches on two things, namely theft and adultery. With respect to the first he says, "If you saw a thief" brought before you for judgment, "you ran with him," not correcting him. Is. 1: "Your princes are faithless." Likewise, "with adulterers you placed your portion," because you do not correct adulterers, but flatter them and cover for them and support them when they come to your notice. Jer. 9: "They are all adulterers." But spiritual theft is when from the words of Sacred Scripture a corrupter steals the true meaning; and thus seeing someone corrupt and conceal the true meaning, and you consenting, you run with him. Jer. 23: "Behold, I am against the prophets who steal my words." Spiritual adultery is when words are twisted to another sense or to another end; for example, if someone preaches for gain or seduction. 2 Cor. 2: "We are not, as many, adulterating the word of God."”

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