1 John 5:8

And there are three that testify in heaven — The testimony of the Spirit, the water, and the blood, is by an eminent gradation corroborated by three, who give a still greater testimony. The Father — Who clearly testified of the Son, both at his baptism and at his transfiguration. The Word — Who testified of himself on many occasions, while he was on earth; and again, with still greater solemnity, after his ascension into heaven, Revelation 1:5; Revelation 19:13. And the Spirit — Whose testimony was added chiefly after his glorification, 1 John 2:27; John 15:26; Acts 5:32; Romans 8:16. And these three are one — Even as those two, the Father and the Son, are one, John 10:30. Nothing can separate the Spirit from the Father and the Son. If he were not one with the Father and the Son, the apostle ought to have said, The Father and the Word, who are one, and the Spirit, are two. But this is contrary to the whole tenor of revelation. It remains that these three are one. They are one in essence, in knowledge, in will, and in their testimony.

It is observable, the three in the one verse are opposed, not conjointly, but severally, to the three in the other: as if he had said, Not only the Spirit testifies, but also the Father, John 5:37; not only the water, but also the Word, John 3:11, John 10:41; not only the blood, but also the Holy Ghost, John 15:26, &c. It must now appear, to every reasonable man, how absolutely necessary 1 John 5:8 is. St. John could not think of the testimony of the Spirit, and water, and blood, and subjoin, "The testimony of God is greater," without thinking also of the testimony of the Son and Holy Ghost; yea, and mentioning it in so solemn an enumeration. Nor can any possible reason be devised, why, without three testifying in heaven, he should enumerate three, and no more, who testify on earth. The testimony of all is given on earth, not in heaven; but they who testify are part on earth, part in heaven. The witnesses who are on earth testify chiefly concerning his abode on earth, though not excluding his state of exaltation: the witnesses who are in heaven testify chiefly concerning his glory at God's right hand, though not excluding his state of humiliation.

1 John 5:6-7 contains a recapitulation of the whole economy of Christ, from his baptism to pentecost; 1 John 5:8 the sum of the divine economy, from the time of his exaltation. Hence it farther appears, that this position of 1 John 5:7-8, which places those who testify on earth before those who testify in heaven, is abundantly preferable to the other, and affords a gradation admirably suited to the subject.