Sacred Tradition refers to the earliest teachings of the original 12 Apostles which were not written down; i.e., veneration of the Virgin Mary, veneration of saints, papl primacy, etc. In the beginning, the teachings were all passed on by oral tradition; eventually some of them were written down and became the New Testament, some of them remained oral. In the Catholic and Orthodox Churches, both carry eaqual weight, and both are used to interpret the other. There is a vast amount of patristic literature to emphasize this point; if you're interested, I would suggest consulting William Jurgen's 3-volume set of The Faith of the Early Fathers, or Johannes Quasten's 4-vlume work, Patrology. Both of them are quite pricey to purchase, so try a library first.
The Bible is not complete in and of itself, in our view. For example, John 21:25 says that not everything Jesus said or did is written down, and Acts 20:35 contains a saying of Jesus not found in the Gospels. Further, Paul tells his audience in 1 Corinthians 11:2, "hold fast to the traditions I handed on to you"; in 2 Thessalonians 2:15 he says "hold fast to tradtions whether oral or by letter"; and in 2 Thessalonians 3:6 he says "shun those not acting according to tradition". Again, there is a vast body of early Christian literature by Origen, Tertullian, Clement, Ambrose, Augustine, Hermas, Ignatius, Cyprian, Polycarp, Justin, and dozens of others to substantiate this.
The Catechism is a compendium of Catholic teaching, collected and refined, over the last 2,000 years. Much of it is Scripture, much of it is Tradition. In addition, it contains the teachings of various Pontiffs, theologians, councils, synods, bishops, saints, abbots, and other authorities within the Church who have issued documents over the centuries. The purpose of the Catechism is to provide a compact, authoritative overview of what the Catholic Church actually teaches and believes. It is not meant to be an end into and of itself, but rather to provide a guideline.
Blessings,
----Wols.
