The letters of John all address a strong challenge to the early church that came from false teachers. They were Gnostics and their teaching was compromising the Gospel. Their main error was in denying that Jesus came in the flesh. Secondly they taught that humans had two distinct parts–body and soul– and that what a person did with one part (the physical) had no bearing on the other part (spiritual). This was a form of dualism that is violently antithetical to the Christian way of life. And third, the Gnostics taught that only formally initiated Gnostics had the truth. (Gnostic means “knowledge.”) All three are serious errors and departures from the Gospel.
The second letter of John, seems to be addressed to a “lady.” But the Greek allows for several interpretations, including that the letter is addressed to the church, which in the Greek has the feminine gender and is described as the “bride” of Christ.
1:7 specifically mentions the error in teaching about Jesus coming in the flesh. John goes beyond the admonition to not believe such teaching. He advises not to allow such a teacher in your house or welcome such a teacher. Why would John be so “inhospitable”? Because the Gospel was at stake. The early church was in its infancy and needed a lot of protection against such heresy so that the message of the Gospel would be rooted and preserved for future generations. This was so that as God promised Abraham from the beginning, that in Abraham (through the Promise of God regarding salvation) ALL the nations of the world would be blessed. Salvation through the Jews is for all people. Throughout the centuries heresy after heresy has been put forth to challenge the simple truth of the Gospel. Jesus is God come in the flesh to save humankind. Believe in Jesus and be saved. Don’t believe and judgment awaits.