'Letters' in the Bible

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

Now if the ministry of death, chiseled in letters on stones, came with glory, so that the Israelites were not able to look directly at Moses’ face because of the glory from his face—a fading glory—

I don’t want to seem as though I am trying to terrify you with my letters.

For it is said, “His letters are weighty and powerful, but his physical presence is weak, and his public speaking is despicable.”

Such a person should consider this: What we are in the words of our letters when absent, we will be in actions when present.