'Letter' in the Bible

not to be easily shaken from your composure or disturbed by any kind of spirit or message or letter allegedly from us, to the effect that the day of the Lord is already here.

Therefore, brothers and sisters, stand firm and hold on to the traditions that we taught you, whether by speech or by letter.

But if anyone does not obey our message through this letter, take note of him and do not associate closely with him, so that he may be ashamed.

I, Paul, write this greeting with my own hand, which is how I write in every letter.