John Chrysostom — as excerpted in the Catena Aurea on John 3:32-36

“(Hom. xxx. 2) i. e. hath shewn that God is true. This is to alarm them: for it is as much as saying, no one can disbelieve Christ without convicting God, Who sent Him, of falsehood: inasmuch as He speaks nothing but what is of the Father. For He, it follows, Whom God hath sent, speaketh the words of God.”