Matthew 21:27

This godless party therefore make answer, and by a seeming humility of speech confessing that they know not, turned to hide their insidious designs. And they answered Jesus, and said, We know not. In saying that they knew not, they lied; and it might have followed upon their answering thus, that the Lord also should say, I know not; but truth cannot lie, and therefore it follows, And he said unto them, Neither tell I you by what authority I do these things. This shows that they knew, but would not answer, and that He also knew, but would not answer, because they would not speak what they knew.

There are two reasons why the knowledge of truth should be kept back from those who ask; either when he who asks is unfit to receive, or from his hatred or contempt of the truth is unworthy to have that which he asks opened to him.

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? "Neither tell I you." For if indeed they had been ignorant it would have been requisite for them to be instructed; but since they were dealing craftily with good reason He answers them nothing.