I have noted in the past that perhaps none of the five Solas constituting the heart of what Kevin Vanhoozer calls “mere Protestant Christianity” is as misunderstood (and for this reason as maligned) as sola Scriptura. Usually objections to this principle trade on a confusion of sola Scriptura (Scripture as the highest authority) with solo or nuda Scriptura (Scripture as the only authority). The former is the true meaning of the phrase (which thus gives full place to interpretive authority in the church), while the latter is a caricature. To be sure, there are some so-called Protestant circles that champion the slogan “no creed but the Bible”, but they do not represent the historic understanding and practice of the church of the Reformation. Thus, if objections are to be raised against sola Scriptura, it is important at least to do so according to its original meaning and not on the basis of twisted or eviscerated versions of it.
There is perhaps no better exponent of sola Scriptura than John Calvin himself, whose view of Scripture is layered, nuanced, and complex. That is to say, Scripture does not reduce, for Calvin, into a text like any other written document that depends on reader interpretation in order to achieve its author’s intended purpose. This does not mean that Scripture need not be interpreted, but that, according to Calvin, Scripture is not inert; it is not simply a book among others whose power lays dormant until activated by its readers. Rather, Holy Scripture, as an inspired text, breathed out from the very mouth of God (2 Tim. 3:16), is “the living voice of God” that speaks “with divine authority”, and thus it cannot be equated with, subsumed under, or domesticated by any other human power or institution, not least the church. The same God who inspired Scripture will not fail to accomplish his purpose in inspiring it. Richard Muller helps us to understand the various contours of Calvin’s view of sola Scriptura when he writes:
Calvin’s arguments for the divinity and authority of Scripture are particularly instructive in view of both their content and their somewhat less than fully systematized character and in view of the relationship indicated by Calvin’s between the self-evidencing authority of Scripture and the internal testimony of the Spirit, on the one hand, and the so-called external evidences of the divinity of Scripture, on the other. Scripture, argues Calvin, is autopiston, self-authenticating, not subject to “proof and reasoning” and having no authority beyond its Word to which believers need turn for validation. Scripture, inasmuch as it is “unassailable truth,” itself provides the norm for judgment:
it is sealed upon our hearts through the Spirit. Therefore, illuminated by his power, we believe neither by our own nor by anyone else’s judgment that Scripture is from God; but above human judgment we affirm with utter certainty (just as if we were gazing upon the majesty of God himself) that it has flowed to us from the very mouth of God by the ministry of men.
This is no static deposit of revelation that Calvin describes, no past manifestation of God’s will duly recorded and embalmed for posterity: Scripture, when read, preached, and heard in faith is the living voice of God speaking with divine authority—so clearly authoritative in its own words and by the Spirit’s testimony in the reading that it is self-authenticating. Here, incidentally, is the link between Calvin’s view of inspiration and his doctrine of the authority of Scripture: the same Spirit that first offered the Word by means of this “ministry of men” continues to work in and through the words upon the hearts of the readers and hearers. It is the same Spirit who “dictates” to his “amanuenses” who continues to testify of the truth of the Word to believers. As the Reformed orthodox would later argue, Calvin indicates that inspiration is the ground of the authority of Scripture: “in order to uphold the authority of Scripture, [the Apostle] declares that it is divinely inspired; for, if it be so, it is beyond all controversy that men ought to receive it with reverence.”
Calvin can, thus, speak objectively of the authority of Scripture, commenting on the apostle’s words in 2 Timothy 3:16, “to assert its authority he teaches that it is inspired of God … dictated by the Holy Spirit.” He also, however, recognizes that this objective authority is not apprehended primarily by empirical analysis of the text as object: “if anyone ask how this can be known, my reply is that it is by the revelation of the same Spirit both to learners and to teachers that God is made known as its author.”
No amount of argument or testimony, Calvin was convinced, would be sufficient “to prove to unbelievers that Scripture is the Word of God … for only by faith can this be made known.” Even so, “Scripture will ultimately suffice for a saving knowledge of God only when its certainty is founded upon the inward persuasion of the Holy Spirit.” The church, therefore, cannot be the guarantor of Scripture inasmuch as the church can only argue and testify to the truth of Scripture in an external way. Indeed, the church itself rests on “the writings of the prophets and the preaching of the apostles,” with the result that the church may proclaim the Word but “the same Spirit … who has spoken through the mouths of the prophets must penetrate into our hearts to persuade us that they faithfully proclaimed what has been divinely commanded.” Those who attempt to “build up faith in Scripture through disputation,” comments Calvin, “are doing things backwards”—since even the successful vindication of Scripture from various attacks will not produce piety in the hearts of those defeated by argument. True conviction of the authority and divinity of Scripture derives from a higher source than mere human argument, “the secret testimony of the Spirit.”
Here we see why Calvin attributed such a high, indeed the highest, place of authority to Holy Scripture not only in but also over the church. The difference between the text of Scripture and any other text written and recognized as authoritative by the church (e.g. the ecumenical creeds) is that Scripture was God-breathed, inspired for the purpose of being the unique vehicle by which God addresses his church with his own “living voice”. For Calvin, there was a direct link between the Spirit’s work of inspiration in the composition of the biblical texts and his continued work of testimony through those texts, a testimony which sets those texts in a position of unparalleled authority. Here we see why Sola Scriptura was not a Protestant innovation; it was the result of careful meditation on what Scripture actually is within the context of God’s communicative action to his people. The Spirit has inspired Scripture to be the means by which he speaks as the living voice of God. Since the same Spirit both inspired Scripture and continually speaks through Scripture, he will not fail in accomplishing the communicative purpose for which he inspired it.
This means, first, that we can affirm, with Calvin, that the Scriptures are ultimately self-authenticating. This is so not only because of the Spirit’s work through Scripture, but also because supreme authority cannot appeal to anything other than itself for its justification. If one authority must appeal to another in order to establish its own credibility and validity, then it is actually the latter, rather than the former, that possesses the greater authority. Scripture, as God’s living voice, cannot therefore be anything other than self-authenticating, for if it required authentication from another source, then it would no longer possess the authority of the God who is greater than all. Thus, however great may be the authority granted by God to the church and its teachers, it must always be reckoned as subservient to the unsurpassable authority of God himself exercised uniquely through Holy Scripture.
Of course it is true that we often find in the New Testament affirmations of the authority of the apostolic tradition. But that is just it: it is the apostolic tradition – what was taught directly from the mouths of the apostles whom Jesus appointed specifically for this task – that possesses this authority, and it is that tradition which has been delivered once and for all to the saints in the pages of Holy Scripture. It is also true that Scripture requires interpretation. Yet that work of interpretation cannot be thought of as completed or definitive, for it is only interpretation. In other words, interpretation is, by definition, subservient to the authority of the text that it interprets. Interpretation does not possess an authority independent of the text that it seeks to understand and explain. Interpretation is only interpretation (and not invention!) if it faithfully exposits the meaning communicated in the text. Thus, far from detracting from Scripture’s supreme authority, the need for interpretation actually intensifies it, for as long as the interpretation of Scripture is subject to error (and the New Testament testifies that it is – 2 Pet. 3:16), it is necessary for the church to remind itself constantly that it can never pronounce the final word on the meaning of Scripture. Only Scripture can pronounce that final word, and it is the work of the Spirit that guarantees that it will.
Once again, it all comes down to faith. Do we believe that God will refuse to allow his inscripturated Word to be domesticated or debilitated by human interpretive error, or do we trust that his living voice will assert itself over against all such errors to accomplish his purpose nonetheless?
 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. pp.257-258. For references to Calvin’s works, see Muller.