1 John 5:6 - Coke's Commentary on the Holy Bible

This is he that came by water and blood— St. John, 1 John 5:5 as well as often elsewhere, intimated that Jesus was the Christ, and that the belief of that article was of the highest moment. Here he is proceeding to the grand evidences of that important truth. The Spirit alone is here said to bear witness, because he was the principal witness; but, 1 John 5:8 the water and the blood are represented as witnesses, together with the Spirit. In John 19:34 the water and blood which came out of Christ's side when he was pierced with the spear, were a clear proof of the reality of his death, and might have taught the Docetae that he had a real body, and really suffered and died; and consequently that his resurrection was a real resurrection.