John Chrysostom

Then exalting them still higher, he even calleth them the epistle of Christ, saying, "Being made manifest that ye are an epistle of Christ." And having said this, he afterwards hence takes ground and occasion for a discussion on the Law. And there is another aim in his here styling them His epistle. For above as commending him, he called them an epistle; but here an epistle of Christ, as having the Law of God written in them. For what things God wished to declare to all and to you, these are written in your hearts. But it was we who prepared you to receive the writing. For just as Moses hewed the stones and tables, so we, your souls. Whence he saith, "Ministered by us."

Yet in this they were on an equality; for the former were written on by God, and these by the Spirit. Where then is the difference? "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." Wide as the difference between the Spirit and ink, and a stony table and a fleshy, so wide is that between these and those; consequently between themselves who ministered, and him who ministered to them.