One of the most pervasive misunderstandings of the Protestant doctrine and practice of sola Scriptura is that such a notion is naive at best and dangerous at worse because it essentially opens the door to any number of contradictory interpretations of Scripture. In other words, to many Roman Catholic ears, sola Scriptura simply sounds like “anything goes” or “everyone’s own understanding of Scripture”. Nothing, however, could be further from the truth. Sola Scriptura is not “solo” or “nuda” Scriptura, as though the Protestant Reformation eliminated all authority in the church with the sole exception of the Bible. Rather, sola Scriptura, correctly understood, entails a reordering of authority into their proper relations. Recognizing that Scripture is the means by which, in Calvin’s words, “God himself speaks in person” to his church, the Reformers acknowledged Scripture as possessing a level of authority higher than that of all other church authorities. At the same time, the Reformers zealously upheld the importance of the early creeds and ecumenical councils, not to mention many of the writings of individual church fathers, as secondary authorities that helped to regulate the right interpretation of Scripture even as they themselves were subject to Scripture’s own regulation. The distinction made was between Scripture as the norma normans non normata – the norming norm that is itself not normed – and church tradition as the norma normata – the normed norm that governs only derivatively. For the Reformers, the secondary authority did govern, yet always in subjection to the authority of God exercised through his Word by the power of the Spirit.
Illustrative of this is Heinrich Bullinger, the Swiss Reformer who succeeded Ulrich Zwingli
in Zurich. Protestant historian Richard Muller provides the following analysis of Bullinger’s view of Scripture, church tradition, and the relation of the two to each other and to the Protestant (i.e. truly catholic) church:
The brief “argument” prefacing Book I of Bullinger’s Compendium is a fairly representative statement of the doctrine of the Reformed churches, already at a rather early stage buttressing the teaching of sola Scriptura with statements concerning the divine authorship, inspiration, and authority of the text:
It behooveth all and every faithful Christian to know, that without all gainsaying, they ought to believe the holy Scriptures of the Bible contained in the old and new Testament. Forasmuch as they are the true word of God, inspired by God, and have of themselves authority and credit, so that it is not needful that they should be made authentic by the Church, or of men. Furthermore, we ought to know, that the said Scripture was truly and uncorruptly written and set forth unto the world, by the holy Prophets and Apostles: and that it doth fully and plainly comprehend, and teach all these things, which are necessary to godliness and salvation: also that the holy Scripture ought to be read, and heard of all men. All causes and controversies of Religion ought to be determined and approved by the holy Scriptures. But such as agree not with these, either are contrary hereunto, of them we ought to beware, whether they be named Traditions or Decrees of Elders, or what name soever they have else. Although the same are either set forth or received by many of few: of learned or of unlearned: although they have been by common consent and custom ever so long received. For the word of God ought by right to be preferred before all other things, inasmuch as the Author thereof is the truth itself, the very eternal and almighty God.
These considerations in no way stand against the use of creeds and confessions in the church as derivative or secondary norms, nor do they in any way indicate a perceived discontinuity on the part of the Reformers between their doctrine and the great tradition of Christian orthodoxy. Thus, Bullinger’s Decades contain a preliminary section, set prior to the first decade of sermons, in which the results of Nicaea, Constantinople, Ephesus and Chalcedon, are exposited and complete texts of their creeds provided together with the creeds from two synods of Toledo, the rules of faith from Ireneus’ Against Heresies and Tertullian’s On the Praescription of Heretics, the Athanasian Creed, the creed of Damasus, bishop of Rome (ca. 376), and the imperial decree concerning the catholic faith from the Tripartite History. Bullinger states in his preface that he has included these works in his theological summation in order to show that Protestant doctrine is indeed the historic teaching of the Church. Even so, Bullinger’s Decades and his related Compendium christianiae religionis, plus Calvin’s Institutes and the Heidelberg Catechism, all follow out the catechetical practice of basing their primary doctrinal exposition on the articles of the Apostle’s Creed…
Bullinger’s expositions of doctrine manifest both a close attention to the scriptural ground of his formulations and a careful use of the tradition. Bullinger has read the fathers closely. He views their interpretation of doctrine as of greatest importance to Christian doctrine—and he frequently dwells on ancient heresies and their refutation as essential to the understanding of the dynamics of correct doctrinal formulation. The issue of the use and abuse of tradition was, therefore, a basic issue to be dealt with among one’s doctrinal presuppositions. Moreover, in all three of his more or less systematic works Bullinger was intent upon demonstrating both in principle and in specific doctrinal argument the continuity of the Reformation with the tradition of patristic interpretation and theology and, therefore, the catholicity of the Reformation. To that end he prefaced his Decades with an essay on the four general councils of the ancient church and with full quotations of their creedal formulations and the rules of faith of several church fathers. Similarly the Confessio is prefaced by a quotation from the Imperial edict of AD 380—the code of Justinian—which defines orthodoxy and heresy in terms of adherence to and departure from the Apostolic faith and the Nicene symbol. Bullinger manifestly belongs to the interpretive model of “Tradition I,” where Scripture provides the absolute norm for doctrine and tradition remains a norm, but clearly subordinated to the biblical standard.
As we can see from this, Bullinger, like the other Reformers, laid great emphasis on the ultimate authority of Scripture, interpreted however in strict continuity with the faith of the one, holy, catholic, and apostolic church. Indeed, the Reformation was a repristination of the earlier orthodox tradition that had been obscured by later deviant tradition. The Roman magisterium had become so swollen with its own subjectivity that it effectively usurped the authority of God by claiming for itself the exclusive right to interpret Scripture and, as a result, it could no longer distinguish the faith inherited from the apostles and the early church from its own aberrant interpolations. For this reason, the Reformers endeavoured, not to dispense with church tradition, but to retrieve its truly orthodox and catholic elements from the quagmire of philosophical, scholastic, and medieval accretions that had hidden them from view. This they did by subjecting medieval Catholicism to the purifying fire of Scripture (the norma normans) and the universal consent of the fathers (the norma normata) in order to expunge the dross and restore the church to its ancient splendor.
The Reformation, therefore, can be seen as a re-catholicizing of the church, bringing it into greater conformity not only with the Word of God (although this was primary) but also with the Apostolic and Nicene-Constantinopolitan-Chalcedonian faith of the early church. Sola Scriptura did not elevate “everyone’s own idiosyncratic interpretation” over “the church’s one infallible teaching”. Rather, it pitted the ultimate authority of “Scripture interpreted according to the universal consent of the fathers” against “Scripture and the fathers distorted by the deviant additions of later tradition”. Despite the ways in which the great Reformation principle may have been abused, this is what sola Scriptura meant then and it is also what sola Scriptura means now.
 Muller, R.A., 2003. Post-Reformation reformed dogmatics: the rise and development of reformed orthodoxy; volume 2: the cognitive foundation of theology 2nd ed., Grand Rapids, MI: Baker Academic. p.72, 353.