the Spirit, the water, and the blood—and these three are in agreement.
8 There are three He applies what had been said of water and blood to it’s own purpose, in order that they who reject Christ might have no excuse; for by testimonies abundantly strong and clear, he proves that it is he who had been formerly promised, inasmuch as water and blood, being the pledges and the effects of salvation, really testify that he had been sent by God.
The faith of the Christian believer (or the believer in Christ) being thus mighty and victorious, it had need to be well founded, to be furnished with unquestionable celestial evidence concerning the divine mission, authority, and office of the Lord Jesus; and it is so; he brings his credentials along with him, and he brings them in a way by which he came and in the witness that attends him.
Commenting on 1 John 5:6-9
And there are three that bear witness on earth,.... To the same truth of the sonship of Christ: the Spirit, and the water, and the blood; by the "Spirit" is not meant the human Spirit or soul of Christ; for however that may be a witness of the truth of his human nature, yet not of his divine sonship: and moreover cannot be said to...