What is the meaning of 2 Thessalonians 2:2?

* The two F.O.G. Bibles & Commentary below are currently a work in progress.

not to be easily disconcerted or alarmed by any spirit or message or letter seeming to be from us, alleging that the Day of the Lord has already come.

Berean Standard Bible (BSB)

not to be quickly shaken in your mind, nor yet be troubled, either by spirit, or by word, or by letter as from us, saying that the day of Christ had come.

World English Bible (WEB)

That{G1519} ye{G5209} be{G4531} not{G3361} soon{G5030} shaken{G4531}{(G5683)} in{G575} mind{G3563}, or{G3383} be troubled{G2360}{(G5745)}, neither{G3383} by{G1223} spirit{G4151}, nor{G3383} by{G1223} word{G3056}, nor{G3383} by{G1223} letter{G1992} as{G5613} from{G1223} us{G2257}, as{G5613} that{G3754} the day{G2250} of Christ{G5547} is at hand{G1764}{(G5758)}.

Strong's King James

(2) that you aren't quickly shaken in the mind! (3) Or to be disturbed either by a ruach-spirit, word or through a letter, as if from us, to the effect that יהוה YAHWEH's Day is present.

The F.O.G*

[2] Don't let your minds be easily unsettled or your hearts filled with anxiety by any message claiming to be prophetic, or any teaching or letter supposedly from us, suggesting that the Day of the Lord has already arrived.

The F.O.G Paraphrase

that ye be not quickly shaken in mind, nor be troubled, neither through spirit, neither through word, neither through letters as through us, as that the day of Christ hath arrived;

Young's Literal Translation