"The task of giving an authentic interpretation of the Word of God, whether in its written form or in the form of Tradition, has been entrusted to the living teaching office of the Church alone. Its authority in this matter is exercised in the name of Jesus Christ." This means that the task of interpretation has been entrusted to the bishops in communion with the successor of Peter, the Bishop of Rome. (CCC P. 85)
"Yet this Magisterium is not superior to the Word of God, but is its servant. It teaches only what has been handed on to it. At the divine command and with the help of the Holy Spirit, it listens to this devotedly, guards it with dedication and expounds it faithfully. All that it proposes for belief as being divinely revealed is drawn from this single deposit of faith." (CCC P. 86)
"Christ the Lord, in whom the entire Revelation of the most high God is summed up, commanded the apostles to preach the Gospel, which had been promised beforehand by the prophets, and which he fulfilled in his own person and promulgated with his own lips. In preaching the Gospel, they were to communicate the gifts of God to all men. This Gospel was to be the source of all saving truth and moral discipline." (CCC P. 75)
In keeping with the Lord's command, the Gospel was handed on in two ways:
Orally "by the apostles who handed on, by the spoken word of their preaching, by the example they gave, by the institutions they established, what they themselves had received — whether from the lips of Christ, from his way of life and his works, or whether they had learned it at the prompting of the Holy Spirit"
In writing "by those apostles and other men associated with the apostles who, under the inspiration of the same Holy Spirit, committed the message of salvation to writing" (CCC P. 76)
"In order that the full and living Gospel might always be preserved in the Church the apostles left bishops as their successors. They gave them their own position of teaching authority." Indeed, "the apostolic preaching, which is expressed in a special way in the inspired books, was to be preserved in a continuous line of succession until the end of time." (CCC P. 77)
This living transmission, accomplished in the Holy Spirit, is called Tradition, since it is distinct from Sacred Scripture, though closely connected to it. Through Tradition, "the Church, in her doctrine, life and worship, perpetuates and transmits to every generation all that she herself is, all that she believes." "The sayings of the holy Fathers are a witness to the life-giving presence of this Tradition, showing how its riches are poured out in the practice and life of the Church, in her belief and her prayer." (CCC P. 78)
"Sacred Scripture is the speech of God as it is put down in writing under the breath of the Holy Spirit." "And [Holy] Tradition transmits in its entirety the Word of God which has been entrusted to the apostles by Christ the Lord and the Holy Spirit. It transmits it to the successors of the apostles so that, enlightened by the Spirit of truth, they may faithfully preserve, expound and spread it abroad by their preaching." (CCC P. 81)
As a result the Church, to whom the transmission and interpretation of Revelation is entrusted, "does not derive her certainty about all revealed truths from the holy Scriptures alone. Both Scripture and Tradition must be accepted and honored with equal sentiments of devotion and reverence." (CCC P. 82)
The Tradition here in question comes from the apostles and hands on what they received from Jesus' teaching and example and what they learned from the Holy Spirit. The first generation of Christians did not yet have a written New Testament, and the New Testament itself demonstrates the process of living Tradition. Tradition is to be distinguished from the various theological, disciplinary, liturgical or devotional traditions, born in the local churches over time. These are the particular forms, adapted to different places and times, in which the great Tradition is expressed. In the light of Tradition, these traditions can be retained, modified or even abandoned under the guidance of the Church's Magisterium. (CCC P. 83)