A letter of unusual serenity addressed to no one in particular — the words in Ephesus are missing from the oldest manuscripts. Whether Paul wrote it is the most evenly balanced authorship dispute in the New Testament.
What the book is
Ephesians is a compact statement of a cosmic reconciliation — Jew and gentile united in one body, the church as the fullness of Christ — followed by ethical instruction including a household code and the passage on spiritual armour.
It has no personal greetings to speak of, no local problems addressed, and no controversy. For a letter supposedly written to a city where Paul spent longer than anywhere else, that absence is striking.
How it is put together
Chapters 1 to 3 are a single sustained theological argument, built from very long sentences — the Greek of chapter 1 runs as one sentence for eleven verses. Chapters 4 to 6 turn to conduct.
The relationship with Colossians is close: roughly a third of Ephesians has a counterpart in Colossians, sometimes in the same order, often with the same wording used for a different purpose.
The authorship and dating question
The words in Ephesus are absent from the earliest and best manuscripts, including P46, and from the original hands of Codex Sinaiticus and Codex Vaticanus. Marcion, in the second century, knew the letter as addressed to Laodicea. The most economical explanation is a circular letter with a blank left for the destination.
Authorship is disputed on grounds that are worth stating plainly, because both sides argue from evidence. Against Pauline authorship: the vocabulary contains many words Paul does not otherwise use, the sentence structure is much heavier than his, the church is treated as universal rather than local, and the relationship to Colossians looks like dependence. For Pauline authorship: ancient attestation is early and unanimous, the differences may reflect a different purpose and an amanuensis, and stylistic arguments from a small corpus are weak.
If Paul wrote it, it belongs to an imprisonment, in the early sixties CE. If not, it belongs to the following generation, roughly 80 to 100 CE. This site treats the question as open, which is what the evidence supports.
Where the external record touches it
Ephesus is one of the best-excavated cities of the Roman east. The temple of Artemis, the theatre where Acts sets the riot of the silversmiths, the library of Celsus and a large residential quarter are all documented, and inscriptions attest the cult of Artemis and the guild structure that the Acts episode assumes.
None of that touches the letter’s contents, which are not about Ephesus. It bears on the setting of Paul’s ministry there as Acts describes it.
The manuscript evidence is the substantive external contribution, and it works against the traditional title: the earliest copies do not carry the address the letter is named after.
Related: the overview of Acts for Paul’s time in Ephesus, and Colossians, the closest parallel text.