For he knew what was in man. As it might be doubted whence Christ obtained this knowledge, the Evangelist anticipates this question, and replies that Christ perceived every thing 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 hold those persons as suspected 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 what is the nature of any one tree. Besides, as Paul tells us, that 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.

Should testify of man - Should give him the character of any man.
He knew what was in man - This he did because he had made all John 1:3, and because he was God, John 1:1. There can be no higher evidence than this that he was omniscient, and was therefore divine. To search the heart is the prerogative of God alone Jeremiah 17:10; and as Jesus knew what was in "these disciples," and as it is expressly said that he knew what was in man - that is, in "all people" - so it follows that he must be equal with God. As he knows "all," he is acquainted with the false pretentions and professions of hypocrites. None can deceive him. He also knows the wants and desires of all his real friends. He hears their groans, he sees their sighs, he counts their tears, and in the day of need will come to their relief.

(7) And needed not that any should testify of man: for he knew what was in man.
(7) Christ is the searcher of hearts, and therefore truly God.

And needed not that any should testify of man,.... Of this or the other man, that he was a good or a bad man; he needed no proofs to be made, or testimonies bore, or evidence given of men's characters and actions; he was of quick understanding, and could distinguish at once between a wicked man and a good man; and so had the characteristic which the Jews require of the Messiah; for they rejected Bar Cozba from being the Messiah, and slew him, because he could not smell, referring to Isaiah 11:3, or discern a bad man from a good man (n); but this Jesus could do, without any external evidence:
for he knew what was in man; which none but the spirit of a man can know; his inward thoughts, the secrets of the heart; thus Christ knew the thoughts of the Scribes and Pharisees, Matthew 9:4, being a discerner of the thoughts, and intents of the heart, Hebrews 4:12. This Apollonius Tyaneus, the ape of Christ, ascribed to himself (o); but is what is peculiar to God; and Christ being God, knows all that is in man; that there is no good in him naturally, nothing but what comes from his Father, is imparted by himself, or implanted by his Spirit; he knows the wickedness there is in man, that his heart is deceitful and desperately wicked, and full of all manner of iniquities; he knows in what condition all the and faculties of the souls of men are; what their affections are set upon, on earthly or heavenly things; whether there is any light in their understandings, or not; whether their wills are subdued and resigned to the will of God, or not; whether their minds and consciences are defiled, or their hearts are sprinkled from an evil conscience; in short, whether the internal good work of grace is begun upon their souls, or not; and he knows the secret springs of all actions, good and bad; all which prove his true and proper deity, and show him to be a suitable Saviour of sinners, and qualify him to be the Judge of the whole earth.
(n) T. Bab. Sanhedrin, fol. 93. 2. (o) Philostrat. Vit. Apollonii, l. 1. c. 13.

knew what was in man--It is impossible for language more clearly to assert of Christ what in Jeremiah 17:9-10, and elsewhere, is denied of all mere creatures.

He - To whom all things are naked, knew what was in man - Namely, a desperately deceitful heart.