John continues his thought from verse 5 (we overcome the world when we believe that Jesus is the Son of God) by launching into an explanation of why we can believe that Jesus is the Son of God and the assurance that comes from that belief.  It is reasonable to believe in Jesus because of the testimony on His behalf.  And belief in that testimony results in assurance for the believer and eternal life from the Father.  Nothing is more important than fully understanding who Jesus is because it is only through Him that we have eternal life.

6-8
John uses what at first seems to be strange language to make a point about the evidence for Jesus being the Son of God (when John discusses Jesus’ identity he is usually careful to use both name and title – Jesus Christ).  He says Jesus is (note the present tense – John makes sure to point out that Jesus is alive) the One who came by water and blood.  What exactly this means is up for some debate, but it probably is a reference to Jesus’ baptism and death (remember that John’s gospel effectively begins with Jesus’ baptism – so it makes sense that he refers to that here).  At Jesus’ baptism God declared Him to be the Son of God and effectively commissioned Him.  It was the beginning of His three-year ministry.  And His death was obviously the culmination of that ministry AND the purpose for His coming.  In His baptism He identified with man’s sin and in His death He delivered man from that sin.  These historical events were necessary for the Messiah to experience and evidence that Jesus is in fact the Christ.

John says the evidence is not only Jesus’ baptism, but His baptism AND death.  This is likely to refute the heresy that Jesus did not retain His divinity when He died on the cross.  The heretics taught that Jesus’ divinity came upon Him at His baptism and left Him before His death.  John makes sure His readers know that He was the Son of God from His birth through His baptism and all the way through His death.  If this were not true, Jesus’ life had little meaning; there is no gospel and nothing for John’s readers – obviously including us – to believe.  It was not enough for Jesus to identify with our sin – He had to conquer it on our behalf.

In verse 7 he adds another element to the testimony for Jesus.  He says the Spirit also bears witness.  Unlike the water and the blood, the Spirit’s witness is an inward testimony.  Jesus’ baptism and death are historical and objective – they are external evidences.  The Spirit, however, is within us and bears witness to us that Jesus is the Messiah.  Earlier John said that believers have an anointing that enables them to know the truth (2:20).  He also said the Spirit’s presence in our lives is proof of our belief (3:24) and evidence that we abide in Christ (4:13).  All these statements allude to the Spirit’s inward testimony in our lives.

Note that he says the Spirit bears witness because the Spirit is the truth.  The Spirit’s nature necessitates that He testify to the person and work of Jesus.  John said in 4:2 that we know the true Spirit because He is the one who confesses that Jesus has come in the flesh.  He is truth and as such cannot help but testify to the truth.  Jesus told His disciples this when He promised them the Spirit in John 15:26-27.

Verse 8 summarizes the three testimonies.  There is objective and subjective evidence that Jesus is the Son of God.  Two testimonies are historical and one is inward.  Three testimonies and all are in agreement.  Under Mosaic Law two witnesses are required to confirm an event (Deut 19:15).  For the divinity of Jesus there are three and they are in perfect agreement.

9-10
John now tells us who is behind the witness of the water and the blood and the Spirit.  The three of them bear witness because of God.  God the Father actually bears witness to the Son through His Spirit, the water, and the blood.  God is the author of the testimony.  Jesus alluded to this when He described His own witness and the Father’s witness as satisfying the law’s requirement for two witnesses (Jn 8:16-18).  The testimony to Jesus’ divinity is ultimately God’s.

This means no one can claim to believe in God and not believe in the Son (see also 2:22-23).  There is no valid belief that says, “I believe in God but do not believe Jesus was the Messiah.”  Or, “I believe in God but do not believe Jesus was a divine sacrifice.”  God the Father is the author of all testimony about His Son – to disbelieve the testimony is to disbelieve God.  This contradicts the heretics of John’s day and any religion that claims belief in God apart from Jesus.

If it is God who testifies to Jesus’ divinity, then the one who believes in Jesus (and this is the purpose of the threefold witness – to prompt faith in the one who hears) is one who believes God’s testimony.  They are actually one and the same – if we believe in the Son we believe in the Father’s testimony about the Son.  And the one who believes has the witness in himself.  God through His Spirit assures the believer his belief is right.  Belief leads to belief (for whoever has, to him shall more be given, and he shall have an abundance – Matt 13:12).  Belief leads to assurance of belief.  That is why the Spirit can be both cause and evidence – the Spirit enables us to believe and then assures us of our belief.  If we have the Spirit we believe and obey.  If we believe and obey it means we have the Spirit.  If we have the Spirit we know we are His (3:24).

If believing in the Son is the same as believing the witness of God, then not believing the Son is the same as calling God a liar.  John once again states truth in a brutally black and white way.  An unbeliever is not neutral – he is one who effectively labels the God of the universe a liar.  We either believe the witness of God or we make Him out to be a liar – there is no neutral ground.

Thought: This is a sobering truth to consider when interacting with the lost.  Our unbelieving friends and family are not simply negligent or apathetic – they are guilty of calling God a liar.  They are in the camp of the Father of Lies.  And as such they deserve the hell that awaits them.  John makes sure we know that belief is not something to be ambivalent about.  Calling the Omnipotent God a liar is a serious offense we cannot take lightly when weighing how bold to be for the gospel.

11-12
The ultimate witness of the Father on behalf of the Son is eternal life given to those who believe.  The ones who believe the threefold testimony of the water and the blood and the Spirit receive in themselves not only assurance that their belief is right but also the gift of eternal life.  Eternal life becomes, then, both gift and witness.  That the believer is granted eternal life is itself God’s witness concerning His Son.  He only gives eternal life to those who have the Son; thus, the Son must be the divine Messiah.

Those who have the Son have the eternal life.  Those who do not have the Son do not have the eternal life.  There is no life apart from the Son and there is no believing in the Son without having the gift of life.  This is why John spends so much time making sure His readers understand who Jesus is.  There is no life apart from Him.  Everything is truly about Him.

This is the third time John has linked eternal life with the Son.  He began the letter by calling Jesus the Word of Life and saying eternal life was manifested in Jesus when He was with the apostles (1:1-2).  He also said that Jesus promised eternal life to His followers (2:25).

Thought: Note that John does not say the one who has the Son will SOMEDAY have eternal life.  He instead says the one who has the Son HAS eternal life.  There are aspects of eternity we experience now.  We have life even in the midst of a fallen world.  Eternal life is perfect and everlasting communion with Jesus in a world without sin (Jesus said in His high priestly prayer – John 17:3 – that eternal life is knowing God the Father and knowing the Son).  While our present communion with Him is not perfect – because we are still affected by sin – that we can have it and have it in abundance is a slice of what is to come.  And while we certainly are not in a world without sin, through Him we have the promise that we can overcome the world (5:5).  He gives us Himself now so we can experience eternity now.  We should meditate on this continually – we have access to eternity NOW.  (And there are people who do not want to be Christians because they think they would have to give up too much!)

It really is ALL about Him.  If there is no eternal life apart from Him there really is no life of any kind apart from Him.  This world and our lives have no meaning without Him.  Apart from Him is only death.  No eternity means no purpose.  No purpose means no life.  And if everything only has value IN Him then everything must center ON Him.  This is why Paul says, “And whatever you do in word or deed, do all in the name of the Lord Jesus, giving thanks through Him to God the Father” (Col 3:17).  Everything in life MUST center on Him because everything in life DOES center on Him.  There truly is no reason to get up in the morning if we get up without Jesus.  As believers we know this and easily give it mental assent – but do we LIVE it?  Do we consciously think as we daily live that nothing has meaning apart from Him and so everything better be grounded in Him?  Do we see EVERYTHING in our lives through the lens of Jesus first, Jesus last, and Jesus only?

Conclusion
John Stott makes the point that this text is really just an elaboration of John’s words in John 20:31 – but these have been written that you may believe that Jesus is the Christ, the Son of God; and that believing you may have life in His name.  God has borne witness to the Son through the Spirit and the water and the blood that we may believe that Jesus is the Son of God.  And when we believe in the Son we have life through Him.  Life comes through belief and belief comes through testimony.

Why is it so important that I should be clear about Jesus Christ?  Why is it I should be certain He is the Son of God, the Christ, the Messiah?  And the witness is this, that God has given us eternal life, and this life is in His Son.  If you have not the Son, you have not life.  “This is my beloved Son, in whom I am well pleased,” God said at His baptism.  He has put it all into Him.  Life is entirely, exclusively, solely, in the Son of God, so that if I am not clear about these facts – that Jesus is the Son of God, and that Jesus is the Christ – then I have not life.  Eternal life is only available as I believe – if I go to Jesus Christ for it.  So unless I can say, “for of His fullness I have received, and grace upon grace” (John 1:16), I am without life, I am dead.  In other words, it is not my belief alone that saves me.  I have received the gift of life, and I can face death and judgment with this evidence that I am a child of God, because in Jesus Christ I have received eternal life, the life of God Himself, in my own soul.  (D Martyn Lloyd-Jones, Life in Christ; 636.)