Jesus has been depicted as a mythical character, a spiritual guru, a visionary, and a charismatic leader who broke off from the Jewish system to create a new sect. The identity and deity of Jesus has been challenged since the first century.
During early Christianity, a teaching was permeating itself in the church. They denied the incarnation of Christ (deity of Jesus) and His resurrection. In a sense, they would elevate their own knowledge at the expense of Christ. They self-proclaimed to have special knowledge that led to moral excellence. However, it was detrimental to the faith of Christians because false teaching leads to false living and a person who denies the deity of Jesus destroys their own faith in Christ.
The Apostle John, the one whom Jesus loved, was a great defender for the deity of Jesus. He would call those who denied Christ, “anti-Christ’s” and “liars” (1Jn 2:4, 2:22, 4:20). John was pointing out their arrogance and their disdain for fellow Christians. He would go on to say that if a person doesn’t love His brother, He cannot love God (1Jn 4:20). That is one of the ways, as well as a confession of Christ, that the Christians could test the spirit (1Jn 4:1-2).
Not everyone who references scripture is honest and a teacher of Truth. Questions should arise if a person proclaims to have special knowledge, does not love those he’s teaching, and proceeds to teach with selfish ambition (Philp. 1:16).
John teaches the deity of Jesus in the beginning of his historical account. John describes Jesus as being God when time began (John 1:1). This is before anything was created so Jesus could not have been created. John also tells us He was the creator of all things when time began (Jn 1:3). Paul describes how Jesus, the creator of all things, was God before coming in the likeness of men (Philp. 2:5-6, Col. 1:16). Jesus Himself declared to be equal with the Father (Jn 10:30). This is illustrated in the Father / Son relationship. Jesus declared it (Matt. 7:21, 10:32, 16:17). The Father Himself would declare Jesus as His Son (Matt. 3:17, 12:18, 17:5).