'Letters' in the Bible

Are we starting to commend ourselves again? Or do we need, like some [false teachers], letters of recommendation to you or from you? [No!]

Now if the ministry of death, engraved in letters on stones [the covenant of the Law which led to death because of sin], came with such glory and splendor that the Israelites were not able to look steadily at the face of Moses because of its glory, [a brilliance] that was fading,

nor do I want to seem to be trying to frighten you with my letters;

for they say, “His letters are weighty and forceful and impressive, but his personal presence is unimpressive and his speech contemptible [of no account].”

Let such people realize that what we say by word in letters when we are absent, is the same as what we are in action when present.