In the King James Version of the Bible these verses read, 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.  7For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost:  and these three are one."

Verse 6:  Jesus "came," or presented Himself to His Father, as well as to the whole world, at the River Jordan by being baptized.  This is how he "came by water."  Although He was "holy, blameless, pure, set apart from sinners" (Heb. 7:26, NIV), He wanted John the Baptist to immerse Him in water to symbolize His complete consecration to do God's will.  But besides coming by water, He came "by blood."  He came to give His life, to shed His blood, to die in place of Adam, redeeming the whole human race.  The Holy Spirit bore witness at the time of His baptism by descending "on him in bodily form like a dove" (Luke 3:22), and the Holy Spirit again bore witness, after our Lord's death and resurrection, when Jesus' followers received the Spirit at Pentecost.  Peter says, "Exalted to the right hand of God, [Jesus] has received from the Father the promised Holy Spirit and has poured out what you now see and hear."  Acts 2:33

Verse 7: This verse needs some extra explanation, as you may have noticed if you've read the scripture in a version of the Bible (NIV, NASB, TEV, RSV, NEB or others) later than the KJV.  The New Testament accounts and letters were copied and recopied, as the years went by, to preserve the information and admonitions given by the apostles and other disciples. These scriptures have provided guidance for the church (and at times the world) down through the ages so that people could get to know the Lord Jesus and learn how to follow Him.  Once in a great while some words were omitted or added by the men copying these manuscripts.  This is the case with most of the words in verse 7, as well as with some in the following verse 8.  These words are not found in any Greek manuscript before the sixteenth century, as noted in the footnotes of many Bible versions.  Verses 7 and 8 should read:  "For there are three that testify: the Spirit and the water and the blood; and the three are in agreement."(NASB)