The one true God has revealed Himself to the Jews. That is why the God of Israel has become the God of all the nations of the world - and this through Jesus Christ.
1) The revelation of God to Abram: “Then the Lord led him outside and said, ‘Look at the heavens and, if you can, count the stars.’ And he said to him, ‘So shall your posterity be…. Abram believed the Lord, who credited the act to him as justice…. “This is my covenant with you: You shall be the father of a multitude of nations; you shall no longer be called Abram, but your name shall be Abraham; for I will make you the father of a multitude of nations. I will make you exceedingly fruitful; I shall make nations of you, and kings shall descend from you.” This is the covenant that is not “testament” but a kind of “bilateralism” - "covenant," - between God and Abram.
Ratzinger (“Many Religions – One Covenant, Israel, the Church and the World”) teases out the distinction between “covenant” and “testament” on the basis of two protagonists of an asymmetrical equality (the notion of person as relation) in the case of covenant – or one principal protagonist who “proclaims” or speaks out His revelation as Old or New “Testaments.” Ratzinger raises the question, “Which is correct? St. Jerome spoke about “New and Old ‘Covenants,’ both in theology and in the liturgy.” He finds that the exegetical scholarship has opted for the correctness of the term “Testament.”
However, the controlling theological epistemology in all of Ratzinger’s thought is the mutuality between Revelation and Faith. Consider his 1956 thesis on Revelation and Faith in the Middle Ages where he discovers in Bonaventure that Revelation did not mean “words” either conceptual or written on a page, but an “act in which God shows himself… And because this is so, the receiving subject is always also a part of the concept of ‘revelation.’ Where there is no one to perceive ‘revelation,’ no re-vel-ation has occurred, because no veil has been removed. By definition, revelation requires a someone who apprehends it. These insights, gained through my reading of Bonaventure, were later on very important for me at the time of the conciliar discussion on revelation, Scripture, and tradition. Because, if Bonaventure is right, then revelation precedes Scripture and becomes deposited in Scripture but is not simply identical with it. This in turn means that revelation is always something greater than what is merely written down. And this again means that there can be no such thing as pure sola scriptura (‘by Scripture alone’), because an essential element of Scripture is the Church as understanding subject, and with this the fundamental sense of tradition is already given.” Attention should be paid to the word “act” that is both on the side of God and the side of the believer. The act in question is the act of self-giving that is the very Person of Christ as revelation of the Father, and the act of self-giving that is the receptivity of Christ within the believer (as in the case of our Lady at the Annunciation). What is in play here is the meaning of person as "act of self-gift" that is the trinitarian prototype of an image as "'work-in-progress."
So also, rather than Old and New “Testaments,” we are dealing with Old and New “Covenants” where there is a certain “equality” between the protagonists – God and man – in the act of revelation and faith.
The large picture that Ratzinger wants to communicate here is that the Covenant between God and Abram is not a testament but a promise that will be existentially and historically fulfilled (because God is faithful to His Word [which is His very Self]) in the New Covenant between Jesus Christ and all men through His Church. The fatherhood of Abram (now become Abraham) will extend far beyond the Jews, and reach all the nations.
2) Babylonian Exile: Judaic faith becomes universalized. The Bible is translated into Greek by the Septuagint. This, of course, means that there will have to be an historical shaping of this universalization since until the time of the Exile to Babylon, the revelation of God was limited to the narrowness of the Jews. But at the time of the exile – and this was the burden of his Regensburg remarks – the faith-experience of the God of Israel was to become a new experience: that of “the God of Israel, an Israel now deprived of its land and worship, was proclaimed as the God of heaven and earth and described in a simple formula which echoes the words uttered at the burning bush: ‘I am.’
“This new understanding of God is accompanied by a kind of enlightenment, which finds stark expression in the mockery of gods who are merely the work of human hands.” Ratzinger goes on: “Thus despite the bitter conflict with those Hellenistic rulers who sought to accommodate it forcibly to the customs and idolatrous cult of the Greeks, biblical faith, in the Hellenistic period, encountered the best of Greek thought at a deep level…”
“Today we know that the Greek translation of the Old Testament produced at Alexandria – the Septuagint – is more than a simple (and in that sense perhaps less than satisfactory) translation of the Hebrew test: It is an independent textual witness and a distinct and important step in the history of Revelation, one which brought about this encounter in a way that was decisive for the birth and spread of Christianity. A profound encounter of faith and reason is taking place here, an encounter between genuine enlightenment and religion.” 
3) The Wise Men From the East: At a third remove, we come to the event of the Epiphany. The Catechism of the Catholic Church (CCC #528) reads:
“The magi’s coming to Jerusalem in order to pay homage to the king of the Jews shows that they seek in Israel, in the messianic light of the star of David, the one who will be king of the nations. Their coming means that the pagans can discover Jesus and worship him as Son of God and Savior of the world only by turning toward the Jews and receiving from them the messianic promise as contained in the Old Testament. The Epiphany shows that the `full number of the nations’ now takes its `place in the family of the patriarchs,’ and acquires Israelitica dignitas (are made `worthy of the heritage of Israel’)
4) The Mission of Jesus: to unite Jews and “pagans:” Ratzinger comments: “In this text, we can see how the Catechism views the relationship between Jews and the nations of the world as communicated by Jesus; in addition, it offers at the same time a first presentation of the mission of Jesus. Accordingly, we say that the mission of Jesus is to unite Jews and pagans into a single People of God in which the universalist promises of the Scriptures are fulfilled that speak again and again of the nations worshiping the God of Israel…. In order to present this unification of Israel, and the nations, the brief text – still interpreting Matthew 2 [the Magi] - gives a lesson on the relationship of the world religions, the faith of Israel, and the mission of Jesus: the world religions can become the star that enlightens men’s path that leads them in search of the kingdom of God. The star of the religions points to Jerusalem, it is extinguished and lights up anew in the Word of God, in the Sacred Scripture of Israel. The Word of God preserved herein shows itself to be the true star without which, or bypassing which, the goal cannot found.”“What does all this mean? The mission of Jesus consists in bringing together the histories of the nations in the community of the history of Abraham, the history of Israel…. The history of Israel should become the history of all, Abraham’s sonship is to be extended to the `many.’ This course of events has two aspects to it: the nations can enter into the community of the promises of Israel in entering into the community of the one God, who now becomes and must become the way of all because there is only one God and because his will is therefore truth for all. Conversely, this means that all nations, without the abolishment of the special omission of Israel, become brothers and receivers of the promises of the chosen People; the become People of God with Israel through adherence to the will of God and through acceptance of the Davidic kingdom.”
5) Jesus Christ is the Meaning of “Man.” The Source for the Universal Truth “Person” Originates in the Experience Self as Gift in Secular Work (= Prayer).
This is derived from an understanding of how human nature was assumed by the divine Person as “his.” The human will does not will in Jesus Christ. He wills with “his” human will. It is a divine Person willing with a human will. That is, He wills as a divine Person wills, but it is humanly. Therefore, the freedom of self-giving that is the meaning of freedom is enhanced and becomes truly itself as image of God, not annulled, in Christ’s human will. So also, the experience of what it means to be “person,” the truth of human personhood, can only be found in the experience of Christ that is self-expropriation (gift).
Consider the case of the three wise men who have left their land, their power and their time to follow the star to the obscure stable in which they are confronted by a child, a young mother, a carpenter, shepherds and animals. Benedict asks: “How was this possible? What convinced the Magi that the Child was ‘the King of the Jews’ and the King of the peoples? There is no doubt that they were persuaded by the sign of the star that they had seen ‘in its rising’ and which had come to rest precisely over the place where the Child was found (cf. Mt. 2, 9). But even the star would not have sufficed had the Magi not been people inwardly open to the truth.”
The conditions of being able to re-cognize the Child in the child are purity and detachment, whereby the self is dispossessed and liberated from itself. Only then can there be the experience and the cognizing in self of that tiny sensible figure who is then re-cognized as Creator of the world hidden in his creation.
This experience of self-expropriation, while yielding a cognizing of the Person of Christ in the child, is an experience and consciousness of self as person imaging the divine Persons. This yield is the self-evident truth of the dignity of the human person and his inalienable rights. This truth is secular, although religiously based. It is not a conceptual truth but a truth of and in consciousness that is the context of all further conceptual thinking. It is the ground of what we understand by “meaning.” This is the truth on which a true globalization can rest, a globalization that will affirm the freedom of autonomy to persons and nations. That truth has been formulated in Gaudium et spes #24: “man, the only earthly being that God has willed for itself, finds himself by the sincere gift of himself.” The ontological reality in play here, the meaning of “to be,” is “to-be-in-relation.” This is mysterious as transcending a proper conceptualizing, but it is not irrational. On the contrary, it is the root and ground of all rationality. It is the truth of faith that makes reason reasonable.
[Finally, consider the "rescue" of the abrahamic covenant by the Logos as both God and man who feeds us with His Flesh and Blood. Ratzinger said: "It is because the Son has handed himself over to God that his 'blood' is now given to men as the blood of the covenant. Body has become word, and word has become body in the act of love that is the specifically divine mode of being...(I)t is important to note that the Last Supper sees itself as making a covenant: it is the prolongation of the Sinai covenant, which is not abrogated, but renewed. Here renewal of the covenant, which from earliest times was doubtless an essential element in Israel's liturgy, attains its highest form possible. In this perspective we should see the Last Supper as one further renewal of the covenant, but one in which, what heretofore was performed ritually, is not given a depth and density - by the sovereign power of Jesus - which could not possibly have been envisaged" (J. Ratzinger, "Many Religions - One Covenant" Ignatius (1999) 60-62).
Previously, Ratzinger said: "When Jesus offers the cup to the disciples and says, 'This is the blood of the covenant,' the words of Sinai are heightened to a staggering realism, and at the same time we begin to see a totally unsuspected depth in them. What takes place here is both spiritualization and the greatest possible realism. For the sacramental blood fellowship that now becomes a possibilitiy brings those who accept it into an utterly concrete - and corporeal - community with this incarnate human being, Jesus, and hence with his divine mystery" (citation above).
 Genesis 15, 5-8;
 Ibid 17, 4-7.
 Ignatius (1999) 47-113.
 J. Ratzinger, “Many Religions – One Covenant,” Ignatius (1999) 48.
 J. Ratzinger, “Milestones…” Ignatius (1997) 108-109.
 Benedict XVI, “The Integration of Faith and Reason,” Regensburg 2006.
 . J. Ratzinger, “Many Religions – One Covenant,” Ignatius (1999) 26.
 Benedict XVI, Solemnity of the Epiphany, Saturday, January 6, 2007.