The term tradition tied to Sacred Tradition does not refer to legends or mythological accounts, nor does it encompass transitory customs or practices which may change, such as styles of priestly dress, particular forms of devotion to saints, or even liturgical rubrics.
Sacred or apostolic tradition consists of the teachings that the apostles passed on orally through their preaching. They have been handed down and entrusted to the Church.
It is necessary that Christians believe in and follow this tradition as well as the Bible. The truth of the faith has been given primarily to the leaders of the Church, who, with Christ, form the foundation of the Church, which has been guided by the Holy Spirit, who protects this teaching from corruption.
Paul illustrated what tradition is: “I commend you because you remember me in everything and maintain the traditions even as I have delivered them to you” (1 Cor. 11:2).
The first Christians “devoted themselves to the apostles’ teaching” (Acts 2:42) long before there was a New Testament.
Paul himself gives a quotation from Jesus that was handed down orally to him: “It is more blessed to give than to receive” (Acts 20:35). This saying is not recorded in the Gospels and must have been passed on to Paul.
Indeed, even the Gospels themselves are oral tradition which has been written down.
Sacred Tradition and Sacred Scripture form one sacred deposit of the word of God. (7:22)