The identity of Jesus Christ is an essential part of His nature which enables people to know how to relate with Him (John 1:14-18; 1 John 1:1-2).  When John wrote his letter, false teachers were claiming that Jesus was merely a man who was anointed with the Holy Spirit at His baptism, but the Spirit left Him before His death.  In other words, they wrongly claimed that Jesus was an ordinary man who was blessed by God for the purpose of His amazing ministry, and then He died as any ordinary man.

However, their teaching defied the truth that Jesus was always God the Son before He came to earth as a baby (John 1:1-3).  They refused to believe that He died as God the Son in order to accept responsibility for all the sins of the world (Colossians 1:19-20).  Jesus came to be baptised in water, not to repent of His own sins but as a pledge that He would allow the guilt of every sinner to cling to Him.  The blood was the blood of the Son of God, which would atone for those sins (1 John 2:2).

Part of the Holy Spirit's work is to assure us that Jesus came as God in the flesh (1 John 4:2), who accepted the punishment that was due to all of us.  It was the reason for His incarnation, and the only means by which sinful people might have the debt of their sins wiped out … enabling peace with God through our Lord Jesus Christ (Romans 5:1).

This false teaching persists today, saying that Jesus was not God … he was a good man who suffered a travesty of justice … that His divine inspiration was temporary until His suffering … and that He was not raised to life again after He died.  Such people reject Christ's incarnation purpose, His substitutionary sacrifice in His role as the total sin-bearer, and His ongoing divine sovereignty … until they reduce Jesus to being a popular moral teacher and miracle-worker.  But they do not have the approval of God's Spirit nor agree with John and other disciples who witnessed His baptism, death, resurrection and ascension.  So, keep true to the evidence from those who were eyewitnesses (2 Peter 1:16).  They wrote it down so that we may believe (and encourage others to believe) that Jesus is the Christ, the Son of God, in order that we and others may enter into His eternal life (John 20:30-31).