Concise Bible Dictionary:
This expression occurs in Romans 2:29; Romans 7:6 and 2 Corinthians 3:6, where the apostle contrasts it with “the spirit”; “the letter killeth, but the spirit giveth life.” Whether of the law or of the gospel, the mere intellectual reception of the words only leads to formality and death; it is only what is “of the Spirit” that can result in life. The Lord is the spirit of all that is written in letters in scripture.
Strong’s Dictionary of Greek Words:
Transliteration:
epistello
Meaning:
from 1909 and 4724; to enjoin (by writing), i.e. (genitive case) to communicate by letter (for any purpose)
KJV Usage:
write (a letter, unto)