The Catholic Church bases her teaching upon one source: The word of God. This divine revelation is transmitted in two ways: through Scripture and apostolic tradition. Many assume that only the writings of the apostles are the word of God. However, their oral transmission of the faith is also considered the word of God (1 Thess. 2:13). Few Protestant groups today accept the validity, let alone the authority, of tradition. In fact, many believe that Scripture is the only definitive source of divine truth.
~ Pope John XXII, in his Bull "Quorumdam exigit" (1317); urging a group of separatist friars who engaged in extreme asceticism to follow the Faith (e.g., Romans 13:1-2) and obey their leaders (from the article "Spirituals")