'Letters' in the Bible

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

that I may not seem as if I desire to terrify you by my letters.

For, "His letters," they say, "are weighty and strong, but his bodily presence is weak, and his speech is despised."

Let such a person consider this, that what we are in word by letters when we are absent, such are we also in deed when we are present.