I am one that bear witness of myself - In human courts a man is not allowed to bear witness of himself, because he has a personal interest in the case, and the court could have no proof of the impartiality of the evidence; but in the case of Jesus it was otherwise. When one has no party ends to serve; when he is willing to deny himself; when he makes great sacrifices; and when, by his life, he gives every evidence of sincerity, his own testimony may be admitted in evidence of his motives and designs. This was the case with Jesus and his apostles. And though in a legal or criminal case such testimony would not be admitted, yet, in an argument on moral subjects, about the will and purpose of him who sent him, it would not be right to reject the testimony of one who gave so many proofs that he came from God.
The Fatherbeareth witness of me - By the voice from heaven at his baptism Matthew 3:17, and by the miracles which Jesus performed, as well as by the prophecies of the Old Testament. We may here remark:
1. that there is a distinction between the Father and the Son. They are both represented as bearing testimony; yet,
2. They are not divided. They are not different beings. They bear testimony to the same thing, and are one in counsel, in plan, in essence, and in glory.

(d) I am one that bear witness of myself, and the Father that sent me beareth witness of me.
(d) The Godhead is plainly distinguished from the manhood, or else there would not be two witnesses: for the accused party is not taken as a witness.

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, beareth 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.

The Father . . . beareth witness. By the prophets, by the works that Jesus does, by his voice at the baptism, and by John the Baptist.