When the Reformers used the words sola Scriptura they were expressing their concern for the Bible’s authority, and what they meant is that the Bible alone is our ultimate authority not the pope, not the church, not the traditions of the church or church councils, still less personal intimations or subjective feelings, but Scripture only. Other sources of authority may have an important role to play. Some are even established by God such as the authority of church elders, the authority of the state, or the authority of parents over children. But Scripture alone is truly ultimate. Therefore, if any of these other authorities depart from Bible teaching, they are to be judged by the Bible and rejected.
James Montgomery Boice, Whatever Happened to the Gospel of Grace? (Wheaton, Ill.: Crossway, 2001), pp. 65-149.