3:1 The preceding verses could have drawn offense from the Corinthians because Paul told them things about himself that they already knew and should have remembered. He mentioned these things as though they were new. He explained that his intention was not to introduce himself to them again in a self-commending fashion. Letters written with pen and ink for this purpose were superfluous since they had already received a much better letter of commendation. He had lived his life among them as an open book.
Representatives of the Jewish authorities in Judea carried letters of commendation (recommendation) to the synagogues of the Dispersion (cf. Acts 9:2; 22:5). The early Christians evidently continued this practice (Acts 18:7; Rom. 16:1). Paul contrasted himself with the legalistic teachers of Judaism and early Christianity who believed that observance of the Mosaic Law was essential for justification and sanctification (cf. Acts 15:5).
3:2 The Corinthians, too, were such letters that God had written. God's method of commending the gospel to others is through the supernatural change that he writes on the lives of believers by His Holy Spirit. In this instance the transformation of the Corinthians' lives was the strongest proof of the genuineness of Paul's apostleship. For Paul to have offered other letters written on paper would have been insulting and superfluous. What God had said about Paul by blessing his ministry with fruit in Corinth spoke more eloquently than any letter that he could have carried on his person.
"Proof of Paul's genuineness was to be found not in written characters but in human characters."119
3:3 Paul's ministry and the ministry of all Christians consists of being the instruments through whom Christ writes the message of regeneration on the lives of those who believe the gospel. He does this by the Holy Spirit.
"The Corinthian church is a letter of which Christ is the author; Paul is either the messenger by whom it was delivered' (Gk. diahonetheisa, ministered' or administered') or perhaps the amanuensis who took it down; it was written not with ink but with the Spirit of the living God.' This contrast between ink' and Spirit' reminds Paul of the contrast between the old covenant and the new, but in view of the material on which the Decalogue, the old covenant code, was engraved, he thinks not of parchment or papyrus (which would have been suitable for ink') but of tablets of stone' as contrasted with tablets of human hearts' (lit. tablets, hearts of flesh') on which the terms of the new covenant are inscribed."120
