John 16:14

But this He spoke of the Spirit, whom those who believed in Him were going to receive; for the Spirit was not yet given, because Jesus was not yet glorified.

“But the Advocate, the Holy Spirit, whom the Father will send in My name, He will teach you all things, and bring to your remembrance all that I said to you.

This is the One who came by water and blood, Jesus Christ; not with the water only, but with the water and with the blood. It is the Spirit who bears witness, because the Spirit is the truth.