Adam Clarke on John 5:34

But I receive not testimony from man [only] - I have no need of John's testimony: the works that I do bear sufficient testimony to me, Joh 5:36.

But these things I say, etc. - You believed John to be a prophet - a prophet cannot lie: he bore testimony that I am the Lamb of God, that beareth away the sin of the world, Joh 1:29; therefore, that ye may be saved by believing in me as such, I have appealed to John's testimony.