Ephrem the Syrian

Then, as for the Gentiles who used to go after gods which were no gods, He Who was God went after them, and by His words, as by a bridle, turned them from many gods to the One. This is that Mighty One, Whose preaching became a bridle in the jaws of the Gentiles, and led them away from idols to Him that sent Him.

Homily On Our Lord 5:1 ↗

Augustine of Hippo

"Be not ye like horse or mule, which have no understanding:" and therefore would govern themselves. But says the Prophet, "Hold in their jaws with bit and bridle." Do Thou then, O God, unto them "that will not come near You" [Psalm 32:9], what man does to horse and mule, that by scourges Thou make them to bear Your rule.

Exposition on Psalm 32 ↗

Ambrose of Milan

Fools then are not free, for it is said to them, Be ye not like to horse and mule, which have no understanding, whose mouths must be held with bit and bridle lest they fall upon thee. Great plagues remain for the ungodly; for they have need of these, in order that their folly may be restrained. It is good discipline which requires this, not severity. Further, he that spareth his rod hateth his son: for a man's own sins scourge him still more severely. …

Letter 37, To Simplician, 41 ↗

Thomas Aquinas

Next, when he says "Do not become," he turns to sinners, that they may return to penance. And concerning this he does two things. First, he sets forth the admonition. Second, the threat, at "With bit." He says therefore: God gives a person understanding, and by understanding he surpasses animals. He who makes himself unworthy of the gift of understanding, therefore, is compared to animals. And so he says, "Do not become like the horse and the mule," etc. …

Exposition on the Psalms of David ↗