Summary: 1) the particulars of the Father’s testimony to the Son (1 John 5:6–9), the apostle reveals 2) the purpose of that testimony (1 John 5:11), and, finally, closes this section by illustrating 3) its power (1 John 5:10, 12).
There is a group of people that claim to be the witnesses of God, they even call themselves Jehovah's Witnesses. And they claim to be propagating the truth that God wants revealed. They claim to be echoing the witness of God. But the truth that God once revealed, the true witness of Jehovah God is that Jesus is the Christ, the Son of God, God incarnate. And the so-called Jehovah's Witnesses are liars because they deny the very thing to which God gives witness in the New Testament,. The Jehovah's Witness religious movement says that Jesus may be called "a" god, small "g," but not THE God. They say He is mighty but not the Almighty. They say He was created by Jehovah, He is not a member of the Trinity, there is no Trinity. They say that the Son during His pre-human state was really an angel by the name of Michael. They further say that the Son did not even possess immortality. He was created and created to die. They teach that when Christ was born of Mary, He ceased being a spirit person all together and became nothing more than a human being…The Jehovah's Witnesses also teach that Jesus became, or took on, the role of Messiah when He was baptized. It was there that God made this human being His spiritual Son. And so He was first a created angel, then a created man, and finally the spiritual Son. The Jehovah's Witnesses deny that Jesus physically, literally arose from the dead. Well you can see from this mish-mash that these people are not Jehovah's witnesses. They are not witnesses of the true God. They do not echo God's witness. They do not echo God's testimony concerning His Son. They are liars and they are representatives of the father of lies, they are the devil's witnesses. And they have many old heresies reframed in their system, very old heresies that come from ancient Gnosticism. (http://www.gty.org/resources/sermons/62-38/the-witness-of-god-part-1)
The apostle John has relentlessly hammered home throughout this epistle the truth that a correct view of the Lord Jesus Christ is essential to salvation (1 John 1:1–4, 2:22, 3:23). In 1 John 4:1–2 John warned his readers against false teachers who deny the truth about Jesus Christ. John began chapter 5 by reminding his readers that only the one who “believes that Jesus is the Christ is born of God” (v. 1), while again we note that verse 13 is the key to the entire letter: “These things I have written to you who believe in the name of the Son of God, so that you may know that you have eternal life” (v. 13). John’s purpose is to demonstrate that there is more than adequate evidence to prove that Jesus is the Son of God who provides eternal life to all who believe in him (Akin, D. L. (2001). 1, 2, 3 John (Vol. 38, p. 195). Nashville: Broadman & Holman Publishers.)
• If we don’t therefore understand the witness of God about His Son then we don’t have eternal life, we will die in our sins, and face the eternal wrath of God. The message of the testimony of God in 1 John 5, not only is the message of life but a message of hope and direction for those who may be deceived, lost or confused.