From Cardinal Jean-Marie Lustiger's Book 'The Promise'
"The Church appears in Jerusalem, after Pentecost, as an "assembly" kahal in Hebrew, ecclesia in Greek. it is unthinkable that she would claim to replace Israel. She is not another Israel, but the very, fulfillment, in Israel, of God's plan...
The Church is then faced with the question of the extent to which these pagans who share in Israel's Election should be obliged to observe the laws which are Israel's trust, responsibility, and privilege. To what extent should these pagans be associated with the totality of Israel's mission? This is the major problem facing the first generations of Christians, as all the New Testament writings testify...
In this early Church, the status of the pagan-Christian assemblies begins to be established. They are not dispensed from observing the Law- if the pagans did not observe the Law, they would have no share in either Israel's Election or grace. But the gift of the Holy Spirit, a grace of the messiah, enables pagans to observe the law differently from Israel, which remains charged with this "delightful" burden of observance. The Church of Jerusalem is, in the Catholic church, the permanence of the promise made to Israel, the presence of the fulfillment of that promise, an attestation of the grace bestowed on the pagans. Thus, the church is that of both Jews and pagans. The fact that this church of Jerusalem was to survive only until the sixth century is one of history's great mysteries and may well be a great spiritual tragedy-whose final outcome remains hidden. For this matter the separation of the church into Eastern and Western branches, cannot be considered settled. These mysteries are a part of the wounds, the sins, that we must acknowledge...
The commandment to love as Jesus loves is not to be substituted for the other commandments. That would make no sense. There is only one holy Law. The law is the revelation of God's commandments. The newness is in God's act, in that he sends Israel his obedient Son. ..Jesus obviously spent much time meditating on the commandments. Everything psalm 119 has to say about the "delights" of the Law was certainly an essential part of his prayer...
The commandments were constantly being meditated by Jesus as word of life...Why do these commandments have such importance? How can we increase our understanding of them? The words from Leviticus – `You shall be holy; for I am holy (11:44;19:2) - are echoed in the Sermon on the Mount... It makes no sense to understand the Sermon on the Mount as the substitution of one commandment for another... It is essential to understand what is meant by the expression "a new law". If the novelty meant is that the Holy Spirit enters the heart of the one who participates in Christ's life – the `law of the spirit' ,as Saint Paul expresses it- then, yes, the expression "new law" is appropriate. However to maintain that the revelation has been substituted for another is to understand absolutely nothing of the mystery of Christ. It is to deny the gift of God. Why have these commandments been given to us?...The Law enables us to act as God acts. And in Jesus meditation, the law reveals how God acts. Just as much as the law is a precept given to man, it is also revelation of God's action and his mystery...How can it be suggested that by observing the Ten Commandments, we act as God does, unless the commandments reveal to us how God acts? We have to enter into Jesus' prayer – the gospel makes it possible – to understand what the commandments tell us about the way God acts, how they allow us to participate in God's own action...
Undoubtedly, there are several ways of observing certain precepts and practices in religious life: that of the Church of Jerusalem, as described in the Acts of the apostles in the first days of Christianity, a community composed of observant Jews; an example of this way today is monastic life – whereas the pagan- Christian communities do not have the same obligations. All however, being ordered by love, which is the greatest good of the church. This diversity is given for the edification of all; but there is only one way to observe the will of God and that is to obey the commandments. " (Cardinal Lustiger "The Promise," JESUS AND THE LAW)
"Pagans also have a right to the Law , as a holy law inscribed in their hearts. It is by acting through the Messiah , with him and in him who made himself obedient to the Law to death on the Cross, that they obey the Law. The discipline of the church dispenses them from Israel's observances, a burden to heavy for them, and which remains Israel's privilege. It is not for the pagans to take on the physical history of the Hebrews, since they, through Christ, have become spiritual offspring of Abraham, but not his physical descendants. Nevertheless, in Christ they have access to the plenitude of the law, and receive the Holy Spirit which allows them to fulfil it." (Cardinal Lustiger "The Promise," ACCESS THROUGH CHRIST TO ALL THE RICHES OF ISRAEL)