1 John 5:7-8 For there are three that testify:the Spirit, the water and the blood; and the three are in agreement.

Had to get my commentary out for this one! Chapters 4 and 5 teach a lot about loving God, believing that Jesus is born of God and loving one another. And in the verse above it says that the Spirit, the water and the blood testify that Jesus is the Son of God. 

In my commentary it states that the Spirit refers to God and we can find His witness in His written Word. The water ,they believe, refers to when Christ was baptized and God opened the heavens and proclaimed that Christ was His Son. Finally, the blood, refers to Christ on the cross. Christ laid down his life; no one took His life from Him; He laid it down by Himself.  If he were a mere man , He could not have done this. 

Don't know how many times I have read this but this one did have me wondering.