1 John 5:8

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 be a witness in earth; rather the Gospel, called the Spirit, which is a testimony of Christ's person, office, and graces and is preached by men on earth; or else the gifts of the Spirit bestowed on men on earth, both in an extraordinary and ordinary way, by which they have been qualified to bear witness to this truth; or it may be the Holy Spirit itself is intended, as he is in the hearts of his people here on earth, where he not only witnesses to the truth of their sonship, but also of the sonship of Christ, and is that witness a believer has within himself of it, mentioned in ( 1 John 5:10 ) . By water is designed, not internal sanctification, which though an evidence of regeneration and adoption, yet not of Christ's sonship; but water baptism, as administered on earth in the name of the Father, and of the Son, and of the Holy Ghost; and which is a noble and standing testimony to the proper, natural, and eternal sonship of Christ: and by "blood" is intended, not justification by the blood of Christ, but rather the blood of the saints, the martyrs of Jesus, who have shed it on earth, in testimony of their faith in the Son of God, and thereby sealing the truth of it; or rather the ordinance of the Lord's supper, which is the communion of the blood of Christ; and represents that blood which was shed for the remission of sins, and has a continual virtue to cleanse from all sin, which is owing to his being the Son of God. The three witnesses on earth seem therefore to be the Gospel, attended with the Spirit and power of God, and the two ordinances of baptism, and the Lord's supper:

and these agree in one;
in their testimony of Christ, the word and ordinances agree together; and the sum and substance of them is Christ; they come from him, and centre in him; they are like the cherubim over the mercy seat, that looked to one another, and to that; and the two ordinances are the church's two breasts, which are equal, and like to one another; there is a great agreement between them, they are like to two young roes that are twins.