Protestant
Why do Catholics follow Sacred Tradition?
The apostles taught both orally and in writing, and Scripture explicitly commands believers to hold fast to what was handed on by word of mouth as well as by letter.
Catholic teaching
Sacred Tradition is the living transmission of the Gospel entrusted by Christ to the apostles and handed down in the Church under the guidance of the Holy Spirit; it is not a separate source of revelation but the same Word of God unfolding through the Church's life, worship, and teaching.
Biblical foundation
Paul praises the Corinthians for maintaining 'the traditions even as I have delivered them to you' (1 Cor 11:2) and John says much of Christ's teaching was never written down (John 20:30, 21:25), implying a body of apostolic teaching transmitted beyond the biblical text.
Scripture references
Historical evidence
Practices such as Sunday worship, infant baptism, and the New Testament canon itself were received and preserved through Tradition long before being formally defined, demonstrating Tradition's essential role even for the most 'biblical' of Christians.
The Church Fathers
“Of the dogmas and messages preserved in the Church, some we possess from written teaching and others we receive from the tradition of the apostles.”