See 1st John 5:6-10
John uses the word "witness" at least 7 times in these few verses. The word witness, means, to testify, to bear record, give testimony, to affirm that one has seen or heard or experienced something, or that he knows it because taught by divine revelation or inspiration. So those definitions are helpful to have in mind as you read through and consider what is taught in this passage.
It begins by giving us some facts about Jesus Christ. First of all, He is a He. That is, He was a real human being, ( as well as being fully God ) He was God come in the flesh. He came by water and by blood. Possibly referring to his water baptism by John, or birth through Mary and then His death on the cross. It could mean, by use of water and blood, just a reference to His physical birth. Either way we know that all three are true, His birth, baptism, and His death. The main point being brought our here is the fact, that it is "The Spirit who bears witness, because the Spirit is truth" By saying the Spirit is truth of course, he is showing that the Holy Spirit's witness cannot be false, as were some of the false prophets, but is to be taken for what it is, and it is truthful.
( As an aside here we see the main ministry of the person of the Holy Spirit, who happens to be in us, and that is, He is bearing witness, he is giving testimony to what and who Jesus Christ is, and what He has done, and what ought to do in relationship to Jesus )
But, going on, There are also three that bear witness in heaven. ( By the way, here John is mentioning this real place called heaven, and is telling us a little about what goes on there )
There are three that are bearing witness in heaven, presumably at all times. The Father, The Word, ( which is Jesus Christ Himself ) and the Holy Spirit, and, John adds these three are one. These three distinct, individual persons are also one. They are each God, and yet they are all God, and they are said to be one, or united in what has been called the God head.
Still more about "witness" There are three that bear witness on earth. The Spirit again, the Water, ( presumably a ref to water baptism of Christ, or the birth of Christ, and then the blood, again presumably referring to His death on the cross. Not completely sure, but either way, both interpretations would be true. One, that Spirit is witnessing about Christ's birth into this world, water and blood, flesh and blood, or He is witnessing about His birth and His death. John adds, that these three are one. Again, there is witness, it's centered in Christ, it involves all the members of the Godhead, and they are united together in what they are witnessing about, what they are declaring, telling us about.
Now John makes some application. Here's the scenario. If we receive the witness or the teaching of mere men, the witness of God is greater. So, man is not as great as God, and God is greater then man. And if both are telling something, we know that God is the greater of the two.
And the witness of God is that He has testified of His Son. That's what God has been testifying of. His Son, Jesus Christ. The man who was God. The God who also became a flesh and blood man. He is the focus of God's testimony.
Lastly, we are told this about "Witness"
He who believes in the Son of God has the witness in himself. He who does not believe God has made Him a liar, because he has not believed the testimony that God has given of His Son.
Since God is greater then man, and if God's testimony differs from man, and man does not accept the testimony from God about Jesus, then the man is in effect, placing himself above God and at the same time declaring that God is not telling the truth. He is saying that God is a Liar, which of course could not be true. Already we were told the Spirit is truth.....and He is one with the Father and the Son. We have been told that there is no darkness in God, in Christ. So, all of them are the same in terms of their purity of character, they are one, or united in who they are as God. Individuals, to be sure, but united together as one God. The 3 fold God head, Father, Son, and Spirit.
They all testify about Jesus Christ.
Pastor Bob Grenier
Calvary Chapel Visalia