An unsigned letter about a split in a community, and the site of the most famous demonstrable insertion in the New Testament — a sentence that entered the Bible in Latin, reached the Greek text in the sixteenth century, and has since been removed again.
What the book is
1 John argues that a group who have left the community were never really part of it, and sets out tests for distinguishing genuine belief and conduct from counterfeit. Its central themes are light, love, and the reality of the incarnation.
It has no address, no named sender, no greeting and no closing greetings. Formally it is not a letter at all; it reads as a written address to a community that already knows who is speaking.
How it is put together
The structure is difficult to outline because it moves in spirals, returning to the same themes in different combinations rather than progressing. This has frustrated commentators for centuries and is a genuine feature of the text, not a failure of analysis.
The relationship to the Gospel of John is close in vocabulary, style and imagery, and the two are usually held to come from the same circle. Whether from the same hand is disputed.
The dating question
The letter is anonymous; the attribution to John comes from later tradition. The dispute it addresses appears to concern the reality of Christ’s physical existence, which points to a controversy of the late first or early second century.
The usual range is 90 to 110 CE, placed relative to the Gospel of John rather than to any external anchor. There is no fixed point, and the range should be read as an estimate.
The Comma Johanneum
1 John 5:7–8 is the clearest case in the New Testament of a passage that can be shown, document by document, to have entered the text late.
In the traditional English Bibles of the sixteenth to nineteenth centuries, these verses contain an explicit trinitarian formula about three that bear witness in heaven. It is absent from every Greek manuscript before the fourteenth century. It appears first in Latin, in Spain, from around the fourth century, and spreads through the Latin tradition. It entered the printed Greek text when Erasmus, having omitted it from his first two editions for lack of Greek support, included it in his third after a Greek manuscript containing it was produced — a manuscript now generally regarded as having been made to order.
Modern critical editions omit it, and modern translations either omit it or footnote it. The point is not that a doctrine falls with it — it does not, since the doctrine rests on other grounds — but that the history of the insertion is fully documented and can be checked by anyone willing to look at the manuscript evidence.
This site treats it as a worked example of what textual criticism actually does, and of why a claim about what the Bible says has to specify which text.
Where the external record touches it
For the contents of the letter, nowhere. For its text, extensively: the Greek manuscript tradition, the Latin versions, and the citations of the passage by early writers are all published and can be consulted, and they are what makes the Comma case decidable.