First Epistle of John different from Gospel of John
The First Epistle of John is the first of the Johannine epistles of the New Testament, and the fourth of the catholic epistles. There is no scholarly consensus as to the authorship of the Johannine works. The author of the First Epistle is termed John the Evangelist, who most modern scholars believe is not the same as John the Apostle. Most scholars believe the three Johannine epistles have the same author, but there is no consensus if this was also the author of the Gospel of John.
This epistle was probably written in Ephesus between 95 and 110 AD. The author advises Christians on how to discern true teachers: by their ethics, their proclamation of Jesus in the flesh, and by their love. The original text was written in Koine Greek. The epistle is divided into five chapters.Purpose
"The Fourth Gospel addresses itself to the challenges posed by Judaism and others outside Johannine circles who have rejected the community's vision of Jesus as preexistent Son, sent by the Father." The New Jerome Biblical Commentary suggests that the three Johannine epistles "describe the fracturing of the Johannine community itself".The author wrote the epistle so that the joy of his audience would "be full" (1:4); that they would "not practice sin" (2:1); that they would not be deceived by false teachers (2:26); and that "you who believe in the name of the Son of God... may continue to know that you have eternal life" (5:13). There are two main approaches to understanding the overall purpose of the letter, tests of life (popularized by Robert Law) and tests of fellowship (popularized by John Mitchell and Zane Hodges). Whereas the Gospel of John was written for unbelievers (John 20:31), this epistle was written to those who were already believers (5:13). Ernest DeWitt Burton found it likely that its audience was largely gentile rather than Jewish, since it contains few Old Testament quotations or distinctly Jewish forms of expression.The epistle also partakes of the debate over Jesus's nature: the debate over "flesh" or the incarnation.  In early Christianity, some advocated for docetism, a view that Christ had been a purely divine being.  Most notably, the group that would eventually become the Gnostics were docetic.  1 John fiercely denounces this belief in favor of the view that Jesus had a real appearance "in the flesh" on Earth.  Chapter 4 writes that "every spirit that confesses that Jesus Christ has come in the flesh is from God" (NRSV), and other passages say that Jesus shed blood, and if he could not shed blood then his death was meaningless.  Chapter 2 also includes a passage that refers to a group of proto-Gnostics: a group that was once with the church but have since left it and deny that the human Jesus was also the spiritual Christ.  The author denounces these secessionists as "antichrists".  The introduction possibly also addresses the issue, especially if the identification of the author as John, or a pseudepigraphic claim to have been a disciple, is assumed: Chapter 1 writes of having evidence of the truth via eyes and touch.  The author may thus be claiming to have known the physical Jesus personally and is emphasizing his physicality as a flesh-and-blood person rather than a spirit or phantasm.