John 5:34

But the witness which I receive is not from man: howbeit I say these things that ye might be saved.

From man ... Thus John the Baptist was not the witness Christ here called on his own behalf. The Saviour did not appeal to human testimony at all.

That ye might be saved ... This explains the reason for the parenthetical statement regarding John, whose witness was indeed mighty and should have been received by the priests. The witness of the great Herald was for the benefit of Israel, and for that purpose Jesus repeated it here; but his office of Messiah rested upon more solid testimony than that of any man.