Apart from the introduction (1:1–4) and conclusion (5:13–21), students of 1 John find little agreement as to how to outline his book. Some see a “spiral” outline in which John repeatedly spirals around themes of doctrine and Christian living. Others see John having a general overview of topics, only then to move more specially into an emphasis on Christian living and then doctrine. Either way, however we outline first John, it is clear that he addresses certain themes and comes back to them again and again throughout his letter. Some of themes include Jesus as the divine Son of God, Jesus as man, love for one another, and keeping God’s commandments.
Rather than attempting to outline the book, we can gather some of its context and primary ideas from four verses in which John himself states why he wrote 1 John.
First, John states in 1 John 1:4, “And we are writing these things so that our joy may be complete”: in context (cf. 1:1–3), this joy is that the readers indeed had fellowship with John and, more importantly, the Father and the Son (cf. 1:1–3).
Second, John states in 1 John 2:1, “My little children, I am writing these things to you so that you may not sin.” The book of 1 John suggests that John was correcting a type of heresy that suggested salvation could be found simply in the reception of an esoteric knowledge given by a nonhuman Christ. When the reality of sin is denied (cf. 1:9), distorted, or dismissed, sin increases in the church. John sought to correct both aberrant doctrine and wayward living.
Third, John states in 1 John 2:26, “I write these things to you about those who are trying to deceive you.” False teachers had crept into the churches, taught false doctrine, left in the wake of the people’s response, and still tried to deceive them thereafter (cf. 2:18–19, 26). John was addressing the persistent problems of these false teachers.
Fourth, John states in 1 John 5:13, “I write these things to you who believe in the name of the Son of God that you may know that you have eternal life.” This verse is often noted as the key verse to 1 John as a whole. Throughout his letter, John indicates that believing certain doctrines (Jesus is man and God) and living in certain ways (e.g., loving one another, keeping God’s commandments) allow one to know with certainty that he has eternal life. Here in 5:13, John points out again that his purpose in writing was to assure believers of their eternal life.