John Calvin Commentary John 2:25

"and because he needed not that any one should bear witness concerning man; for he himself knew what was in man." — John 2:25 (ASV)

For he knew what was in man. Since it might be doubted from where Christ obtained this knowledge, the Evangelist anticipates this question and replies that Christ perceived everything in men that is concealed from our view, so that He could on His own authority make a distinction among men. Christ, therefore, who knows the hearts, had no need of any one to inform Him what sort of men they were. He knew them to have such a disposition and such feelings that He justly regarded them as persons who did not belong to Him.

The question put by some—whether we too are authorized by the example of Christ to consider those persons suspect who have not given us proof of their sincerity—has nothing to do with the present passage. There is a wide difference between Him and us; for Christ knew the very roots of the trees, but, except from the fruits which appear outwardly, we cannot discover the nature of any one tree. Besides, as Paul tells us, charity is not suspicious (1 Corinthians 13:5), we have no right to entertain unfavorable suspicions about men who are unknown to us. But, that we may not always be deceived by hypocrites, and that the Church may not be too much exposed to their wicked impostures, it belongs to Christ to impart to us the Spirit of discretion.