Ye are our epistle
Here a reason is given why they stood in no need of letters of commendation, to or from the church at Corinth, because that church was their living epistle, and which was much preferable to any written one. The apostle calls them their epistle in the same sense, as they are said to be his "work in the Lord, and the seal of his apostleship", ( 1 Corinthians 9:1 1 Corinthians 9:2 ) they were so as persons regenerated by the Spirit and grace of God, in whose conversion he was an instrument; now it was the work of conversion in them, which was the epistle said to be
written in our hearts;
some think it should be read, "in your hearts"; and so the Ethiopic version reads it; and it looks as if it should be so read, from the following verse, and from the nature of the thing itself; for the conversion of the Corinthians was not written in the heart of the apostle, but in their own; and this was so very notorious and remarkable, that it was
known and read of all men;
everyone could read, and was obliged to acknowledge the handwriting; it was so clear a case, what hand the apostle, as an instrument, had in the turning of these persons from idols to serve the living God; and which was so full a proof of the divinity, efficacy, truth, and sincerity of his doctrine, that he needed no letters from any to recommend him.