Thirteen verses from someone who calls himself only the elder, to a congregation addressed as a lady. It is a note about hospitality, and about withholding it.
What the book is
2 John is a brief letter from the elder to the elect lady and her children — almost certainly a congregation and its members rather than an individual. It urges love, warns about people who deny that Christ came in the flesh, and instructs the readers not to receive such teachers into the house or greet them.
It is one of the two shortest books in the Bible and fits on a single sheet of papyrus, which is probably not a coincidence.
How it is put together
It follows the ordinary conventions of a Greco-Roman letter closely: sender, addressee, greeting, body, closing wish to visit in person rather than write more. That formal regularity is a contrast with 1 John, which has none of it.
The overlap with 1 John in vocabulary and concerns is substantial, and the two are conventionally read together.
The dating question
The writer identifies himself only as the elder, and the identification with the author of the Gospel of John or with the apostle is traditional rather than stated. Papias, quoted by Eusebius, refers to an elder John distinct from the apostle, which is the origin of a long-running discussion that has never been settled.
The letter is placed with 1 John and 3 John, in the range of roughly 90 to 110 CE, on the basis of shared concerns rather than any independent evidence.
Why a short note matters
The instruction not to receive certain teachers is the most historically informative thing in the letter. Early Christian communities were connected by travelling teachers who depended on hospitality, and hospitality was therefore the mechanism by which a network either spread a teaching or refused it.
Withholding a greeting sounds trivial and was not: it was the practical means of exclusion available to a congregation with no other enforcement. The letter is a small window onto how these groups actually governed themselves.
Where the external record touches it
Nothing external attests this letter or its situation. Its early manuscript attestation is thin, as one would expect for a text this short, and it was among the books whose canonical status was discussed rather than assumed in the early centuries.
The Didache, an early Christian manual of uncertain date, gives detailed rules for testing travelling teachers and limiting their stay. It is not evidence about 2 John, but it documents the same practice from another angle and is worth reading alongside it.