John Chrysostom

And how was it they did not say that the baptism was of men? "They feared the people" it is said. Seest thou a perverse heart? In every case they despise God and do all things for the sake of men. For this man too they feared for their sakes not reverencing the saint but on account of men; and they were not willing to believe in Christ, because of men, and all their evils were engendered to them from hence. After this, because they, dealing craftily, said, "We know not," He said not, neither know I, but what? …

Homily on the Gospel of Matthew 67 ↗

Jerome

He also said to them: Neither do I tell you by what authority I do these things. They answered and said to him: We don't know. Then Jesus also replied to them: Neither do I tell you by what authority I do these things. But the Truth cannot lie, and he said: Neither do I tell you. From this, he shows that they know but refuse to answer, and he knows but refuses to say, because they keep silent about what they know. …

Commentary on Matthew ↗

Thomas Aquinas

Then the responses are treated. And first, the response of the Jews; secondly, of Christ. It is true that the lesser people believed, but the Pharisees were indignant; therefore, if they said it was from men, their confusion would follow. Likewise, all held John to be a prophet; above (11:7): "What went you out into the desert to see?" etc.

Commentary on Matthew ↗