'Letters' in the Bible

For in our letters we say no other things to you, but those which you are reading, and to which you give agreement, and, it is my hope, will go on doing so to the end:

Do we seem to be again attempting to put ourselves in the right? or have we need, as some have, of letters of approval to you or from you?

For if the operation of the law, giving death, recorded in letters on stone, came with glory, so that the eyes of the children of Israel had to be turned away from the face of Moses because of its glory, a glory which was only for a time:

That I may not seem to have the desire of causing you fear by my letters.

For his letters, they say, have weight and are strong; but in body he is feeble, and his way of talking has little force.

Let those who say this keep in mind that, what we are in word by letters when we are away, so will we be in act when we are present.