Jesus said frequently „You have heard …, but I tell you … He thus changes many of the statements of the Old Testament. Is this not a rejection of the Old Testament?
Jesus Christ was critical of the traditions of the old (Mark 7:3.5) because he saw that many Jews and Jewish teachers of his time had put the traditions of men in the place of Gods law. But Jesus was no iconoclast who wanted to overturn everything. With many of his teachings he adhered to the traditions of his people, indeed, he drew heavily from Holy Scriptures, the so called Old Testament. In place of the rabbinic interpretation, however, he supplied his own: But I tell you (Matthew 5:22 and others). He wants to say: „I tell you what the real and true tradition is. Furthermore: I am the tradition, the living and life giving passing on of tradition (Katholischer Erwachsenen-Katechismus (German Cathoic Adult-Catechism), p. 51. (See: www.vatican.va/archive/ENG0015/__PR.HTM)
It would, however, be a grave misunderstanding to assume that Jesus Christ’s claim to being the true explanation of the Old Testament, indeed, to be its goal and its centre, was a call to abandoning the Old Testament. The “Catechism of the Catholic Church” comments on this important area of teaching:
“121 The Old Testament is an indispensable part of Sacred Scripture. Its books are divinely inspired and retain a permanent value, for the Old Covenant has never been revoked.
122 ‚Indeed, „the economy of the Old Testament was deliberately so oriented that it should prepare for and declare in prophecy the coming of Christ, redeemer of all men." "Even though they contain matters imperfect and provisional," the books of the Old Testament bear witness to the whole divine pedagogy of God's saving love: these writings "are a storehouse of sublime teaching on God and of sound wisdom on human life, as well as a wonderful treasury of prayers; in them, too, the mystery of our salvation is present in a hidden way. (Dei Verbum 15)
123 Christians venerate the Old Testament as true Word of God. The Church has always vigorously opposed the idea of rejecting the Old Testament under the pretext that the New has rendered it void (Marcionism).[…]
128 The Church, as early as apostolic times, and then constantly in her Tradition, has illuminated the unity of the divine plan in the two Testaments through typology, which discerns in God's works of the Old Covenant prefigurations of what he accomplished in the fullness of time in the person of his incarnate Son.
129 Christians therefore read the Old Testament in the light of Christ crucified and risen. Such typological reading discloses the inexhaustible content of the Old Testament; but it must not make us forget that the Old Testament retains its own intrinsic value as Revelation reaffirmed by our Lord himself. Besides, the New Testament has to be read in the light of the Old. Early Christian catechesis made constant use of the Old Testament. As an old saying put it, the New Testament lies hidden in the Old and the Old Testament is unveiled in the New.
130 Typology indicates the dynamic movement toward the fulfilment of the divine plan when "God [will] be everything to everyone." Nor do the calling of the patriarchs and the exodus from Egypt, for example, lose their own value in God's plan, from the mere fact that they were intermediate stages.”