'Letters' in the Bible

Do we begin again to commend ourselves? or do we need, as some, commendatory letters to you, or commendatory from you?

(But if the ministry of death, in letters, graven in stones, began with glory, so that the children of Israel could not fix their eyes on the face of Moses, on account of the glory of his face, a glory which is annulled;

that I may not seem as if I was frightening you by letters:

because his letters, he says, are weighty and strong, but his presence in the body weak, and his speech naught.

Let such a one think this, that such as we are in word by letters when absent, such also present in deed.