'Letters' in the Bible

Are we beginning to commend ourselves again? Or [do we], like some, need letters of recommendation to you or from you?

But if the ministry of death in letters carved on stone came with glory, so that the sons of Israel were not able to look intently into the face of Moses because of the glory of his face, which was transitory,

so that I do not want to appear as if I were terrifying you by my letters,

because it is said, "His letters [are] severe and powerful, but his bodily presence [is] weak and his speech is of no account."

Let such a person consider this: that what we are in word by letters [when we] are absent, [we will] also [be] in {actions} [when we] are present.