Matthew Poole and continuators on John 5:32

32 There is another that beareth witness of me , and I know▪ that the witness which he witnesseth of me is true .

The Father by a voice from Heaven testified of Christ, that he was his well-beloved Son, in whom he was well pleased, Mat. 3.17. Some understand it of Iohn the Baptist, of whom he speaketh, v. 33. But he naming Iohn in the next verse, it seems most proper to understand this of the Father testifying of Christ, both at his Baptism, and also at his Transfiguration▪ and to Interpret the next Verse, as speaking of another Testimony distinct from that of Iohn

And (saith our Saviour) I know; that is, I am fully assured that his Testimony of me is true; for God is that God who cannot lye, but is truth it self. So that I do not barely testifie of my self; for my Father, whom you all own to be a God of truth, and who cannot lye, and whom I know to be such, he testifieth of me, and none can contradict his Testimony.

Marginal references: Mat. 17.5.