In my post “The Bible Alone” I offered a definition of sola scriptura as “the belief that the Bible alone is the final and infallible authority in matters of Christian faith and that tradition, reason and emotions, though important, must ultimately be evaluated in light of Scripture.”
I later deleted the words “and infallible” from that definition because they seemed to add unnecessary confusion. The Reformers didn’t view Biblical inspiration (a belief held by all Christians) as necessitating a belief in the absolute inerrancy and infallibility of Scripture. The modern Evangelical conceptions of inerrancy and infallibility are products of nineteenth century reactions against modernism and are foreign to the theological foundations of the Reformation.
The Reformers framed sola scriptura against the absolute and infallible teachings and traditions of the Church. The Church at that time (and the Roman Catholic Church today) recognized the authority of Scripture on the basis of it having been recognized as authoritative by the Church — that is, the Church gave the Bible its authority. Luther found that belief deeply troubling, especially in light of the significant corruption that plagued the Church at that time. He held that final authority is to be found only in the Word of God — that is, in God Himself as revealed in Jesus Christ — and that Scripture provides the best witness to this Gospel. For Luther, the Bible, insomuch as it offers an inspired revelation of God incarnate, has authority over the fallible traditions and teachings of the Church. Likewise, Calvin believed that the Spirit worked through Scripture — that the authority of Scripture is derived from its divine inspiration and not by means of the authority of the Church.
But Luther and Calvin did not reject tradition outright (as did some radical Anabaptists); both valued it greatly as a necessary aspect of Christian life — just not as the final standard by which we are to find God.
Sola scriptura means connecting with the fullness of God as found in Jesus Christ and as conveyed through Scripture. When we subvert that revelation of the Gospel by substituting tradition or personal preference for the Word of God, we are substituting ourselves for God. And when we substitute a personal and dogmatic devotion to a written text alone for the fullness of the Gospel as contained in Christ, we forgo sola scriptura and embrace idolatry.