So then, brothers and sisters, stand firm and hold fast to the teachings we passed on to you, whether by word of mouth or by letter.
NIV
So then, brethren, stand firm and hold fast to the traditions and instructions which you were taught by us, whether by our word of mouth or by letter.
AMP
Therefore, brethren, stand fast, and hold the traditions which ye have been taught, whether by word, or our epistle.
KJV
You show that you are a letter from Christ, the result of our ministry, written not with ink but with the Spirit of the living God, not on tablets of stone but on tablets of human hearts.
NIV
You show and make obvious that you are a letter from Christ delivered by us, not written with ink but with [the] Spirit of [the] living God, not on tablets of stone but on tablets of human hearts. [Exod. 24:12; 31:18; 32:15, 16; Jer. 31:33.]AMP
Forasmuch as ye are manifestly declared to be the 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 fleshy tables of the heart.
KJV