“This is He that came by water and blood, even Jesus Christ; not by water only, but by water and blood. And it is the Spirit that beareth witness, because the Spirit is truth.  For there are three that bear record in Heaven, the Father, the Word, and the Holy Ghost: and these three are one.  And there are three that bear witness in earth, the Spirit, and the water, and the blood: and these three agree in one.

If we receive the witness of men, the witness of God is greater: for this is the witness of God which He hath testified of His Son.

He that believeth on the Son of God hath the witness in himself: he that believeth not God hath made Him a liar; because he believeth not the record that God gave of His Son.  And this is the record, that God hath given to us eternal life, and this life is in His Son.

He that hath the Son hath life; and he that hath not the Son of God hath not life.” 1 John 5:6-12 (KJB)

From the Geneva Bible Translation Notes for 1 John 5:6…

“(8) This is he that came by water and blood, [even] Jesus Christ; (9) not by water only, but by water and blood. And it is the (g) Spirit that beareth witness, because the Spirit is truth.

(8) He proves the excellency of Christ, in whom only all things are given us by six witnesses, three heavenly, and three earthly, who wholly and completely agree together. The heavenly witnesses are, the Father who sent the Son, the Word itself, which became flesh, and the Holy Spirit. The earthly witnesses are water, (that is our sanctification) blood, (that is, our justification) the Spirit, (that is, acknowledging of God the Father in Christ by faith) through the testimony of the Holy Spirit. (9) He warns us not to separate water from blood (that is sanctification from justification, or righteousness, begun from righteousness imputed) for we do not stand on sanctification, but so far as it is a witness of Christ’s righteousness imputed to us: and although this imputation of Christ’s righteousness is never separated from sanctification, yet it is the only matter of our salvation.

(g) Our spirit which is the third witness, testifies that the holy Sprit is truth, that is to say, that that is true which he tells us, that is, that we are the sons of God.” Geneva Bible Translation Notes