John 19:34 But one of the soldiers with a spear pierced his side, and forthwith came there out blood and water. 35 And he that saw [it] bare record, and his record is true: and he knoweth that he saith true, that ye might believe.
We know he also send His Spirit ,so there are three witnesses IN the one (Jesus) .They came out of Him (the one) on this earth.
5 Who is he that overcometh the world, but he that believeth that Jesus is the Son of God? ;
6 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.
7 For there are three that bear witness in earth, the spirit, and the water, and the blood: and these three agree in one.
He came through water =natural life,birth
through blood (that is the life too but he leaves it here)
He send his Spirit to bear witness in us
We have the testimony of the Water after regeneration
We have the testimony that the Son of God poured Ηis blood, His life for us
And the Spirit gives that information of the sacrifice and the things to come (the glory of the Son)