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.
In keeping with the biblical injunction that “every fact is to be confirmed by the testimony of two or three witnesses” (2 Cor. 13:1; cf. Deut. 19:15; Matt. 18:16; 1 Tim.5:19; Heb. 10:28), John presents three aspects of God’s witness to Jesus Christ. Then, after delineating 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).
1) The Particulars of God’s Testimony (1 John 5:6–9)
1 John 5:6–9 6 This is he who came by water and blood—Jesus Christ; not by the water only but by the water and the blood. And the Spirit is the one who testifies, because the Spirit is the truth. 7 For there are three that testify: 8 the Spirit and the water and the blood; and these three agree. 9 If we receive the testimony of men, the testimony of God is greater, for this is the testimony of God that he has borne concerning his Son. (ESV)
In 1 John 5:1–5, John described the joys and blessings of overcomers, those who believe that Jesus Christ is the Son of God. But the apostle knew that many would ask why they should believe that Jesus is who John claimed Him to be. After all, Israel rejected Him; “He came to His own, and those who were His own did not receive Him” (John 1:11). The Jews contemptuously referred to Him as a lying deceiver (Matt. 27:63), guilty of leading the people astray (John 7:12, 47; Luke 23:2) and of fomenting insurrection against Rome (Luke 23:5; cf. John 11:47–48). They blasphemously accused Him of being a glutton and a drunkard (Matt. 11:19), of being insane (John 10:20; cf. Mark 3:21), and, most heinous of all, of being demon-possessed (John 8:48; cf. v. 52; 7:20; Matt. 9:34; 10:25; 12:24; cf. vv. 31–32). Ultimately, their murderous hatred of Jesus led them to call for His crucifixion (Matt. 27:22–23). Why then, in light of Israel’s rejection, should anyone believe that Jesus Christ is the Messiah, God Incarnate, the only Savior of sinners? Because of the infallible, unassailable, incontrovertible testimony of God Himself. The pre-existent Son of God, was sent from heaven by God to do His will. He came to earth to fulfill His Mission. In His fulfillment of it, two events are prominent: the Baptism by which He was consecrated to His Messianic work, and the Passion by which He completed His work of atonement and propitiation (Brooke, A. E. (1912). A critical and exegetical commentary on the Johannine epistles (p. 131). New York: C. Scribner’s Sons.)