In the ChristianNew Testament, the First Epistle of John is the fourth catholic or "general" epistle. Written in Ephesus about AD 100-110, the epistle is traditionally attributed to John the Evangelist, also the traditional author of the Gospel of John and the other two epistles of John. Not actually an epistle (or letter), the work is a sermon written to counter heresies that Jesus did not come "in the flesh," but only as a spirit. It also defines how Christians are to discern true teachers: by their ethics, their proclamation of Jesus in the flesh, and by their love.
The epistle is traditionally held to have been written by John the Evangelist, and probably also at Ephesus, and when the writer was in advanced age. The epistle's content, language and conceptual style indicate that it may have had the same author as the Gospel of John, 2 John, and 3 John. Modern scholars believe that the apostle John wrote none of the New Testament books traditionally attributed to him.
The author wrote the Epistle so that the joy of his audience would "be full" (1.4) and that they would "sin not" (2.1) and that "you who believe in the name of the Son of God... may know that you have eternal life." (5.13) It appears as though the author was concerned about heretical teachers that had been influencing churches under his care. Such teachers were considered Antichrists (2.18-19) who had once been church leaders but whose teaching became heterodox. It appears that these teachers taught that JesusChrist was a Spirit being without a body (4.2), that his death on the cross was not as an atonement for sins (1.7) and that they were no longer able to sin (1.8-10). It appears that John might have also been rebuking a proto-Gnostic named Cerinthus, who also denied the humanity of Christ.
The purpose of the author (1:1-4) is to declare the Word of Life to those to whom he writes, in order that they might be united in fellowship with the Father and his Son Jesus Christ. He shows that the means of union with God are, (1) on the part of Christ, his atoning work (1:7; 2:2; 3:5; 4:10, 14; 5:11, 12) and his advocacy (2:1); and (2), on the part of man, holiness (1:6), obedience (2:3), purity (3:3), faith (3:23; 4:3; 5:5), and love (2:7, 8; 3:14; 4:7; 5:1).
On the whole, therefore, the evidence seems to me to be clear that this passage is not a genuine portion of the inspired writings, and should not be appealed to in proof of the doctrine of the Trinity.
↑"Although ancient traditions attributed to the Apostle John the Fourth Gospel, the Book of Revelation, and the three Epistles of John, modern scholars believe that he wrote none of them." Harris, Stephen L., Understanding the Bible (Palo Alto: Mayfield, 1985) p. 355