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.
Protestants claim the Bible is the only rule of faith, meaning that it contains all of the material one needs for theology and that this material is sufficiently clear that one does not need apostolic tradition or the Church’s magisterium (teaching authority) to help one understand it. In the Protestant view, the whole of Christian truth is found within the Bible’s pages. Anything extraneous to the Bible is simply non-authoritative, unnecessary, or wrong—and may well hinder one in coming to God.
The Protestant Reformers said that the Bible is the sole authoritative source of religious truth, whose proper understanding must be found by looking only at the words of the text itself. This is the Protestant teaching of sola scriptura (Latin: by Scripture alone). According to this teaching, no outside authority may mandate an interpretation, because no outside authority, such as the Church, has been established by Christ as an arbiter to determine which of the conflicting interpretations is correct.