Now that we’ve been given the five sources, the Church is careful to illustrate that the boundaries between them are stark or well-defined. To the contrary, catechesis is a “living tradition” that incorporates the Bible, the liturgy, two millennia of bishops and theologians, and the lived witness of saints:
96. These are all the sources, principle or subsidiary, of catechesis but must not be understood in a narrow sense. (General Catechetical Directory, 45b) Sacred Scripture “is the speech of God as it is put down in writing under the breath of the Holy Spirit”, (Dei Verbum 9) Sacred Tradition “transmits in its entirety the word of God which has been entrusted to the apostles by Christ the Lord and the Holy Spirit”. (Dei Verbum 9) The Magisterium has the duty of “giving an authentic interpretation of the word of God”, (Dei Verbum 10b) and in doing so fulfils, in the name of Christ, a fundamental ecclesial service. Tradition, Scripture and the Magisterium, all three of which are closely connected, are “each according to its own way”, (Dei Verbum 10c) the principle sources of catechesis. Each of the subsidiary sources of catechesis has its own proper language which has been shaped by a rich variety of “documents of the faith”. Catechesis is a living tradition of such documents: (cf. Synod of Bishops, Message to the People of God 9) biblical excerpts, liturgical texts, patristic writings, formulations of the Magisterium, creeds, testimonies of the saints and theological reflections.
The living source of the word of God and the “sources” deriving from it, and through which it is expressed, provide catechesis with those criteria for the transmission of its message to all who have made their decision to follow Jesus Christ.