In this chapter, Paul continues the theme of sincerity in preaching the Gospel, saying that they themselves (those converted by him) were his guarantee of honesty, in his preaching of a system far more glorious than that of the Mosaic Law.
A believer, desiring to enter the communion of a church where he is not known, should submit a letter of introduction or recommendation, as did Phoebe (Romans 16:1-2) and Apollos (Acts 18:27). The Lord Jesus himself presented His credentials (John 5:3-47). However, Paul says that he himself did not need such a letter to the believers at Corinth, for they themselves were his "letter" (being themselves his converts) that everyone could read. They were the work of the Holy Spirit, Who had written His message in their hearts, and, by the same divine power, Paul was able to do his job.
Here Paul makes a contrast between the two "alliances" that form the main subject of the Bible - the Old Covenant of the Law, given by God to Israel through the mediation of Moses, and the New Covenant (Matthew 26:28; Mark 14:24, Luke 22:20), made between God and the believers in Christ, the Lord Jesus himself being the Mediator (Hebrews 9:15).
The Old Covenant, demanding perfect obedience to the Mosaic law (called here "the letter" because it was written by God on two stone tablets on Mount Sinai), was undoubtedly His own glory, which showed itself in the face of Moses when he descended from the Mount (Exodus 34:29-35). But that glory was temporary and gradually disappeared from the face of Moses, thus indicating that the Alliance of the law was transient (13).
Even so, the Alliance of Law had its glory (11), it was perfect, being established by God - but it was impossible for men to keep it, because of their sin. The Jews still read (in the synagogues) the Old Covenant as their justification before God, not understanding that Christ has removed the veil of ignorance (14).
The hearts of the Jews are still in locks, not realizing that the Mosaic law never will bring justification before God. However, when a Jew converts to the Lord Jesus, he recognizes that he is justified, not for doing the work required by the Mosaic law, but by his faith in Christ (15-16).
This understanding and conversion form the work of the Spirit of the Lord who frees us from the condemnation of the Mosaic Law (17) and thus, being able to clearly understand, we can recognize the glory of the Lord and be transformed by the Holy Spirit to be more and more similar to Lord in our character (18).
1 Do we begin again to commend ourselves? Or do we need, as some others, epistles of commendation to you or letters of commendation from you?
2 You are our epistle written in our hearts, known and read by all men;
3 clearly you are an epistle of Christ, ministered by us, written not with ink but by the Spirit of the living God, not on tablets of stone but on tablets of flesh, that is, of the heart.
4 And we have such trust through Christ toward God.
5 Not that we are sufficient of ourselves to think of anything as being from ourselves, but our sufficiency is from God,
6 who also made us sufficient as ministers of the new covenant, not of the letter but of the Spirit; for the letter kills, but the Spirit gives life.
7 But if the ministry of death, written and engraved on stones, was glorious, so that the children of Israel could not look steadily at the face of Moses because of the glory of his countenance, which glory was passing away,
8 how will the ministry of the Spirit not be more glorious?
9 For if the ministry of condemnation had glory, the ministry of righteousness exceeds much more in glory.
10 For even what was made glorious had no glory in this respect, because of the glory that excels.
11 For if what is passing away was glorious, what remains is much more glorious.
12 Therefore, since we have such hope, we use great boldness of speech—
13 unlike Moses, who put a veil over his face so that the children of Israel could not look steadily at the end of what was passing away.
14 But their minds were blinded. For until this day the same veil remains unlifted in the reading of the Old Testament, because the veil is taken away in Christ.
15 But even to this day, when Moses is read, a veil lies on their heart.
16 Nevertheless when one turns to the Lord, the veil is taken away.
17 Now the Lord is the Spirit; and where the Spirit of the Lord is, there is liberty.
18 But we all, with unveiled face, beholding as in a mirror the glory of the Lord, are being transformed into the same image from glory to glory, just as by the Spirit of the Lord.
2 Corinthians chapter 3