'Epistle' in the Bible

Ye are our epistle, written in our hearts, known and read of all men;

being made manifest that ye are an epistle of Christ, ministered by us, written not with ink, but with the Spirit of the living God; not in tables of stone, but in tables that are hearts of flesh.

For though I made you sorry with my epistle, I do not regret it: though I did regret it (for I see that that epistle made you sorry, though but for a season),