testify. bear witness. See note on John 1:7.
what was in man. This attribute elsewhere attributed only to Jehovah (Jeremiah 17:10; Jeremiah 20:12). Here this knowledge was universal ("all", John 2:24), and individual ("man ").
Related Commentaries of John 2:25
John 2:25
25 And needed not that any should testify of man: for he knew what was in man.