2 Corinthians 3:3

And that the Spirit lays hold on the flesh, he says in the same Epistle, "That ye axe the epistle of Christ, ministered by us, inscribed not with ink, but with the Spirit of the living God, not in tables of stone, but in the fleshly tables of the heart." If, therefore, in the present time, fleshly hearts are made partakers of the Spirit, what is there astonishing if, in the resurrection, they receive that life which is granted by the Spirit?

These are the laws of reason, words that impart inspiration, written by the hand of the Lord, not on tablets of stone but inscribed in the hearts of men, provided only that those hearts are not attached to corruption. Therefore, the tablets of the hard of heart have been broken, that the faith of little ones might be formed in impressionable minds. Both laws served the Word as means of educating humanity, the one through Moses, the other through the apostles. But what a means of education is the one given through the apostles!

Now we have not received this longing from God on the condition that it should not or could not ever be satisfied.… So when even in this life men devote themselves with great labor to sacred and religious studies, although they obtain only some small fragments out of the immeasurable treasures of divine knowledge, yet [they gain this advantage, that] they occupy their mind and understanding with these questions and press onward in their eager desire. Moreover they derive much assistance from the fact that by turning their mind to the study and love of truth they render themselves more capable of receiving instruction in the future. For when one wishes to paint a picture, if he first sketches with the faint touch of a light pencil the outlines of the proposed figure and inserts suitable marks to indicate features afterward to be added, this preliminary drawing with its faint outline undoubtedly renders the canvas more prepared to receive the true colors. So it will be with us, if only that faint form and outline is inscribed "on the tablets of our heart" by the pencil of our Lord Jesus Christ.… It is clear, then, that to those who have now in this life a kind of outline of truth and knowledge there shall be added in the future the beauty of the perfect image.

As the pen is an instrument for writing when the hand of an experienced person moves it to record what is being written, so also the tongue of the just man, when the Holy Spirit moves it, writes the words of eternal life in the hearts of the faithful, dipped "not in ink but in the Spirit of the living God." The scribe, therefore, is the Holy Spirit, because he is wise and an apt teacher of all. And the Spirit writes swiftly, because the movement of his mind is swift. The Spirit writes thoughts in us, "not on tablets of stone but on fleshy tablets of the heart." In proportion to the size of the heart, the Spirit writes in hearts more or less, either things evident to all or things more obscure, according to the heart's previous purity. Because of the speed with which the writings have been finished, all the world now is filled with the gospel.

The things which are promised are eternal and are therefore said to be written with the Spirit of God, unlike temporal things written in ink, which fades and loses its power to record anything.

For we do not judge the heavenly commands by the ears of the body, but since it is the word of God, certain notions of good and evil have sprung up in us; while that which is evil, we naturally understand should be avoided, and that which is good, we naturally understand should be commanded. Therefore, in this, we seem to hear the voice of the Lord, which prohibits some things and commands others. And so, if anyone does not obey those things which we believe have once been commanded by God, he is considered subject to punishment. However, the commandment of God is not written with ink on stone tablets, but is impressed in our hearts by the spirit of the living God. Therefore, our own opinion becomes its own law. For if the Gentiles, who do not have the law, naturally do what the law requires, they themselves are a law to themselves, who show the work of the law written on their hearts. Therefore, human opinion is to itself as the law of God.

By this finger, as we read, God wrote on the stone tablets which Moses received. For not with a finger of flesh did God make the forms and elements of those letters which we read; by his Spirit he gave the law. And so the apostle said: "For the law is spiritual, which indeed is written not with ink but with the Spirit of the living God; not in tables of stone but in fleshly tables of the heart." For, if the letter of the apostle is written in the Spirit, what stands in the way of our being obliged to believe that the law of God was written not in ink but in the Spirit of God, which surely does not stain the secrets of our heart and mind but illuminates them?

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.

It was clear to everybody that the Corinthians owed their conversion to Paul's teaching, which the Holy Spirit had confirmed. We know that we belong to Christ if we have received the Spirit.

Paul shows how much better the grace of the Spirit is than the law and how much higher the preaching of the apostles is than the dispensation of the prophets.

Forgetting the false teachers, Paul goes on to the heart of the matter and expounds the difference between the two Testaments.

In what way? In that the law of Christ and His commandments, like written letters, abide and are preserved in you.

Having taken the opportunity to compare the Law with the Gospel, he makes here such a comparison: as Moses was a minister of the Law, so we too are ministers of your faith in the Gospel, and as he engraved on stone tablets, so we engrave on your hearts; the Law was written with ink, but the Gospel is written in you by the Spirit. Therefore, as much as the Spirit differs from ink and the heart from stone, so much does the New Testament differ from the Law. Since hardened people have hearts of stone, he called the hearts of believers fleshly, because they are receptive to the word.

Then he explains how this letter is known, saying, you show that you are a letter from Christ, and in regard to this he does three things. First, he explains whose letter it is; secondly, how it was written; thirdly, on what. He shows whose it is when he says, from Christ. Hence, he says, you show that you are a letter from Christ, i.e., informed and led by Christ, principally and authoritatively: "For you have one teacher" (Matt. 23:8), but by us secondarily and instrumentally. Hence he adds, delivered by us: "This is how one should regard us, as servants of Christ" (1 Cor. 4:1); "What then is Apollos? What is Paul? Servants through whom you believed" (1 Cor. 3:5) He shows how it was written, not with ink, i.e., not mixed with errors, as the letters of the false apostle; not changeable and imperfect as the Old Law, which led no one to perfection (cf. Heb. 7:19); for black ink is that by which error is understood, and delible by which changeableness is understood. It is written not with ink, I say, but with the Spirit of the living God, i.e., by the Holy Spirit, by whom you live and by whose teaching you have been instructed: "In whom you were sealed with the promised Holy Spirit" (Eph. 1:13). He suggests where it is written, when he says, not on tablets of stone, as the Old Law, to exclude hardness; as if to say: not in the stony hearts of the hard-hearted, as the Jews: "You stiff-necked people, uncircumcised in heart and ears, you always resist the Holy Spirit" (Ac. 7:51); but on tablets of human hearts, i.e., hearts opened by charity, and human, i.e., made receptive as a result of filling and understanding: "I will take out of your flesh the heart of stone and give you a heart of flesh" (Ez. 36:26).