A major tenet of Protestant theology is the authority and finality of the biblical revelation. This principle is often poorly stated but the essential point is that Scripture serves as the supreme court in all matters of faith and practice.
For some all one needs to do is quote a verse and the issue is settled. For others they are aware of the difficulty of some questions and realize Scripture does not directly address some doctrinal and ethical issues with complete clarity. The Westminster Confession of Faith puts this principle rather clearly:
All things in Scripture are not alike plain in themselves, nor alike clear unto all; yet those things which are necessary to be known, believed, and observed, for salvation, are so clearly propounded and opened in some place of Scripture or other, that not only the learned, but the unlearned, in a due use of the ordinary means, may attain unto a sufficient understanding of them.
Here, and elsewhere, the Reformation doctrine of sola scriptura reflects a nuanced tension between the perspicuity (clarity) of Scripture necessary for final authority, and the occasional need for its meaning to be revealed by careful exposition (Hebrews 5:12).
The errors made by many Protestants regarding this truth are too numerous to engage in through one post. They are legion and they are often extreme.
Sola scriptura teaches that the only doctrines which should be admitted or confessed are found directly within Scripture or indirectly therein by using valid logical deduction or valid deductive reasoning discovered within scripture. But, and this is vitally important, sola scriptura is not a denial of other authorities governing Christian life and devotion! This is the error large numbers of modern evangelicals have made by appealing wrongly to sola scriptura. What the principle simply says is that all other authorities are subordinate to, and to be corrected by, the written word of God.
Another major error is to believe that sola scriptura ignores Christian history and tradition when interpreting the Bible. In principle the doctrine sees the Bible as the only final authority in matters of faith and practice but not the only authority. Martin Luther thus said, "The true rule is this: God's Word shall establish articles of faith, and no one else, not even an angel can do so.
One of the more important aspects of this doctrine is the idea of efficacy of Scripture. Scripture, united with the power of the Holy Spirit, not only demands, but creates the acceptance of its clear teaching. Thus a proper teaching of Scripture produces faith and obedience. The Holy Scripture is not a dead letter, an academic tool box. By the power of the Holy Spirit inherent in its witness it is powerful and living in the human soul. Put more clearly, Scripture compels more than intellectual assent to its doctrine. By the power of the Spirit it works to create the living agreement of faith. The Smalcald Articles affirm, "in those things which concern the spoken, outward Word, we must firmly hold that God grants His Spirit or grace to no one, except through or with the preceding outward Word.” This statement does not deny that divine revelation comes through other means (e.g., in nature, etc.) but simply affirms that the spoken teaching of the Christian faith must firmly hold to the canon of the written Scriptures and then proceed in the power of the Spirit.
I do not write these things to debate with Catholic apologists, though they any are welcome to disagree and post their response. What I write these things to establish a basic principle, one I believe taught by the Reformers and the early church Fathers as well. While Luther’s doctrine of faith, at least as he put it, is not clearly found in the writings of the earliest Christian theologians (Alister McGrath has established this beyond any reasonable doubt in his magnum opus, Iustitia Dei: A History of the Christian Doctrine of Justification), the doctrine of the authority and finality of the Holy Scripture is abundantly evident in the writing of early church fathers. Consider these few quotations:
We have received the disposition of our salvation by no others, but those by whom the Gospel came to us; which they then preached, and afterwards by God's will delivered to us in the Scriptures, to be the pillar and ground of our faith. (St. Irenaeus, Lib. III. c. 1)
Let the shop of Hermogenes prove that what it advances is written; or if it be not written, let it fear the malediction uttered against those who dare to add or to retrench. (Tertullian c. 160-240, adv. Hermog.)
There is one God, whom we do not otherwise acknowledge, brethren, but out of the Sacred Scriptures. For as he, who would profess the wisdom of this world cannot otherwise attain it, unless he read the doctrines of the philosophers; so whosoever will
exercise piety towards God, can learn it no where but from the Holy Scriptures. (St. Hippolytus c. 170-c.235, adv. Noetum, c. IX)
In the two testaments every word that pertaineth unto God may be sought and discussed, and out of them all knowledge of things may be understood. And if anything remains which Holy Scripture does not determine, no other third scripture ought to be received to authorize any knowledge, but we must “commit to the fire” what remains, that is, reserve it unto God. (Origen c. 185-c.254, Hom. in Lev.)
When I arrived in the district of Arsinoe, when as you know this notion had long been widely held, so that schisms and secessions of entire churches had taken place, I called a meeting of the presbyters and teachers of the village congregations, with any laymen who wished to attend, and urged them to thrash out the question in public. So they brought me this book as positive and irrefutable proof, and I sat with them for three days on end from
dawn to dusk, criticizing its contents point by point. In the process I was immensely impressed by the essential soundness, complete sincerity, logical grasp, and mental clarity shown by these good people, as we methodically and good-temperedly dealt with questions, objections, and points of agreement. We refused to cling with pig-headed determination to opinions once held even if proved wrong. There was no shirking of difficulties, but to the limit of our powers we tried to grapple with the problems and master them; nor were we too proud, if worsted in argument, to abandon our position and admit defeat; conscientiously, honestly, and with simple-minded trust in God, we accepted the conclusions to be drawn from the proofs and teachings of Holy Writ. (Eusebius, in The History of the Church, quoting Dionysius c. 200-c. 265, bishop of Alexandria)
The holy and divinely inspired writings are sufficient of themselves alone to make known the truth. (St. Athanasius 296-373, Orat. Contr. Gent. Tom. I)
If you desire a new quotation, if you pretend to affirm anything besides what is written, why do you dispute with us, who are resolved to hear nothing, and to say nothing, besides what is written? (St. Athanasius, De Incarn. Chr.)