1 John 5:6
This is he that came by water and blood, even Jesus Christ; not by water only, but by water and blood…
There are five respects in which that Divine agent may be represented as bearing witness to Christ.
(1) He bore witness by the types and prophecies of the Jewish dispensation — both of which foretold Christ's advent, character, and work.
(2) He bore witness by qualifying Christ, as man, for His mediatorial offices (Isaiah 11:1-3).
(3) The Spirit bore witness to Christ by the signs and wonders which He enabled the apostles to perform in attestation of their Divine commission.
(4) He bears witness to Christ in that Holy Bible which so clearly and impressively unfolds His glory and His grace.
(5) He bears witness also by "revealing God's Son in" the soul — by bringing the gospel practically to bear on the understanding, the conscience, and the heart.
(A. S. Patterson, D. D.)
Parallel VersesKJV: 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.