It is precisely because of this personal experience of relationship with Jesus Christ that Paul henceforth places at the centre of his Gospel an irreducible opposition between the two alternative paths to justice: one built on the works of the Law, the other founded on the grace of faith in Christ. The alternative between justice by means of works of the Law and that by faith in Christ thus became one of the dominant themes that run through his Letters: "We ourselves, who are Jews by birth and not Gentile sinners, yet who know that a man is not justified by works of the law but through faith in Jesus Christ, even we have believed in Christ Jesus in order to be justified by faith in Christ, and not by works of the law; because by works of the law no one will be justified" (Gal 2: 15-16). And to the Christians of Rome he reasserts that "all have sinned and fall short of the glory of God, they are now justified by his grace as a gift, through the redemption which is in Christ Jesus" (Rm 3: 23-24). And he adds "we hold that a man is justified by faith apart from works of the law" (ibid., v. 28). At this point Luther translated: "justified by faith alone". I shall return to this point at the end of the Catechesis. First, we must explain what is this "Law" from which we are freed and what are those "works of the Law" that do not justify. The opinion that was to recur systematically in history already existed in the community at Corinth. This opinion consisted in thinking that it was a question of moral law and that the Christian freedom thus consisted in the liberation from ethics. Thus in Corinth the term "πάντα μοι έξεστιν" (I can do what I like) was widespread. It is obvious that this interpretation is wrong: Christian freedom is not libertinism; the liberation of which St Paul spoke is not liberation from good works.

So what does the Law from which we are liberated and which does not save mean? For St Paul, as for all his contemporaries, the word "Law" meant the Torah in its totality, that is, the five books of Moses. The Torah, in the Pharisaic interpretation, that which Paul had studied and made his own, was a complex set of conduct codes that ranged from the ethical nucleus to observances of rites and worship and that essentially determined the identity of the just person. In particular, these included circumcision, observances concerning pure food and ritual purity in general, the rules regarding the observance of the Sabbath, etc. codes of conduct that also appear frequently in the debates between Jesus and his contemporaries. All of these observances that express a social, cultural and religious identity had become uniquely important in the time of Hellenistic culture, starting from the third century B.C. This culture which had become the universal culture of that time and was a seemingly rational culture; a polytheistic culture, seemingly tolerant constituted a strong pressure for cultural uniformity and thus threatened the identity of Israel, which was politically constrained to enter into this common identity of the Hellenistic culture. This resulted in the loss of its own identity, hence also the loss of the precious heritage of the faith of the Fathers, of the faith in the one God and in the promises of God.

Against this cultural pressure, which not only threatened the Israelite identity but also the faith in the one God and in his promises, it was necessary to create a wall of distinction, a shield of defence to protect the precious heritage of the faith; this wall consisted precisely in the Judaic observances and prescriptions. Paul, who had learned these observances in their role of defending God's gift, of the inheritance of faith in one God alone, saw this identity threatened by the freedom of the Christians this is why he persecuted them. At the moment of his encounter with the Risen One he understood that with Christ's Resurrection the situation had changed radically. With Christ, the God of Israel, the one true God, became the God of all peoples. The wall as he says in his Letter to the Ephesians between Israel and the Gentiles, was no longer necessary: it is Christ who protects us from polytheism and all of its deviations; it is Christ who unites us with and in the one God; it is Christ who guarantees our true identity within the diversity of cultures. The wall is no longer necessary; our common identity within the diversity of cultures is Christ, and it is he who makes us just. Being just simply means being with Christ and in Christ. And this suffices. Further observances are no longer necessary. For this reason Luther's phrase: "faith alone" is true, if it is not opposed to faith in charity, in love. Faith is looking at Christ, entrusting oneself to Christ, being united to Christ, conformed to Christ, to his life. And the form, the life of Christ, is love; hence to believe is to conform to Christ and to enter into his love. So it is that in the Letter to the Galatians in which he primarily developed his teaching on justification St Paul speaks of faith that works through love (cf. Gal 5: 14).

Paul knows that in the twofold love of God and neighbour the whole of the Law is present and carried out. Thus in communion with Christ, in a faith that creates charity, the entire Law is fulfilled. We become just by entering into communion with Christ who is Love.

[Pope Benedict, General Audience 19 November 2008]