1 John has no opening greeting, no named sender, and no named recipient, which has led most scholars to treat it as a circulating theological tract or sermon rather than a letter in the ordinary sense, even though tradition groups it with the epistles. Its immediate occasion is a split within the community: "they went out from us, but they did not belong to us," the text says of some who had left, and much of the letter answers a teaching those who left apparently held, that Christ had not truly come "in the flesh," an early denial of Christ's full humanity that later theology would call docetism.
Against this, 1 John insists that whoever denies the Son does not have the Father either, and grounds its authority in eyewitness testimony, "what we have heard, what we have seen with our eyes, what we have looked at and touched with our hands." The letter's most enduring theological claim is its double definition of God as love, "God is love," stated twice, in chapter 4, tying right belief about Christ directly to loving one's fellow believers as an inseparable test of genuine faith: "those who say, I love God, and hate their brothers or sisters, are liars." The letter closes with an unusually direct offer of assurance, writing "so that you may know that you have eternal life," a stated purpose rare in the New Testament's more argumentative epistles.