Rivals' Messiahs

Sources: Marianne Meye Thompson, 1-3 John (IVP, 1992); Bart Ehrman, Lost Scriptures: Books that Did Not Make It into the New Testament (Oxford, 2003); I. Howard Marshall et al., Exploring the New Testament: A Guide to the Letters and Revelation (IVP, 2002), chapter 21.

The Nature of Christian Understanding
Teachings concerning Jesus proliferate in Christian circles:

Gnostic Gospels (e.g., Secret Book of James, Gospel of Thomas, Book of Thomas, Gospel of Truth, Gospel of Mary, Second Treatise of the Great Seth),
compilations of legends (e.g., Infancy Gospel of Thomas, Acts of Paul and Thecla), and
apocalypses (e.g., Secret Book of John, Apocalypse of Peter).

Anticipating this (or responding to earlier instances of it), 1-3 John address consequences of conflict, schism, and secession among followers of Jesus with radically different theologies and self-understandings (1 John 2:18-19, 2:26, 4:1-5).

The Integrity of the Gospel: 1 John
The letters use themes common in the Fourth Gospel: life, eternal life, truth, light, Jesus as Son of God, the Father and the Son, Jesus laying down his life, salvation as 'knowing God', remaining in Christ, Jesus' new commandment, and the world (Marshall, 290).
But schism makes these 'essentially contested concepts'. How can they be intelligible in the wake of division?

These letters appeal to the tradition itself to adjudicate differences.

The letters remind the remnants of the character of true Christian faith:

Jesus is the Messiah (1 John 2:22, 4:2),
God is light (1:5, 2:7-11),
God is love (3:10-24, 4:16-5:5).

Ethics follows theology: Each of these truths becomes the 'indicative' of an 'indicative-imperative'.
Four ethical signs assure believers of communion with God:

We obey his commandments (1 John 2:3).
We reflect God's and Christ's character (2:29, 3:2-3, cf. 3:4-10).
We love one another (3:14).
We are given his Spirit (3:23-24, 4:13).

The center of disciples' attention is the indicatives; the imperatives follow.
Whoever they are, the false teachers' teachings and lives lack this integrity (1 John 1:8-10, 2:4-6, 2:9, 2:22-23, 4:1-3, 4:20, 2 John 7).
Christian faithfulness, truthfulness, and love are literally the moral of the gospel story.
Thus integrity, not just information, is essential to Christian understanding.