John Gill Commentary John 8:18

"I am he that beareth witness of myself, and the Father that sent me beareth witness of me." — John 8:18 (ASV)

I am one that bear witness of myself
As he does of his sonship, in (1 John 5:7) .

And the Father that sent me, bears witness of me ;
as he did, by the descent of the Spirit upon him at his baptism, and by a voice from heaven, both at that time, and at his transfiguration, and by the miracles which he wrought; and particularly he bore testimony of him, long before, in prophecy, that he was the light of the world he now said he was, (Isaiah 42:6) ;

so that here were two testifiers, his Father and himself; which show them to be two distinct divine persons, and equal to each other: and now if the testimony of two men is true, firm, and authentic, and to be depended upon and received, then much more the testimony of two divine persons; see (1 John 5:9) .