By the word of the Lord the heavens were made, and by the breath of his mouth all their host…For he spoke, and it came to be; he commanded, and it stood firm. (Psalm 33:6, 9)
In the beginning was the Word, and the Word was with God, and the Word was God. (John 1:1)
You have been born again, not of perishable seed but of imperishable, through the living and abiding word of God. (1 Peter 1:23)
Sometimes in interconfessional discussions (or debates) about the Word of God and its place in the church, we can tend to focus so much on questions such as the authority of tradition and the problems of interpretation that we neglect what is perhaps the most critical issue: what exactly is the Word of God? Is it ‘just a book’ that does not become “living and active, sharper than any two-edged sword” (Heb. 4:12) until properly wielded in the hands of those uniquely authorized to do so? Or is this too reductive of a definition? It seems to me that until we are clear on what the Word of God is, we will be unable to come to agreement on its position and role in the church.
The Swiss theologian Karl Barth, respected across confessional lines, is particularly remembered for his theology of the Word of God which he unfolded in a threefold manner as the Word revealed, written, and proclaimed (in that order). Since for Barth, the Word of God revealed in the person and work of Jesus Christ is absolutely primary (for no other Word existed in the beginning with and as God!), the Word cannot be reduced to what is written in Scripture or proclaimed by the church. Since the Word of God is first and foremost the Word who is God through whom and for whom all things came into being, it possesses the aseity and eternality of God and is, properly speaking, identical with the living and efficacious action of God in creating, ruling, and redeeming all things. Barth explains (and I quote at length):
When God speaks, there is no point in looking about for a related act. The fear that talk might be “only” talk is, of course, only too apposite in relation to human speech. When man speaks, then his misery, the rift between truth and reality in which he lives, is plainly exposed, and the more so the better and more beautifully and truly he speaks….When God speaks, however, the fear is groundless. The man who has heard God speak and might still ask about the related act is simply showing that he has not really heard God speak. We can hear Christian sermons and ask what really happens as they take place. What does actually correspond to all these words? This is a question well worth putting. We can even hear Holy Scripture and simply hear words, human words, which we either understand or do not understand but along with which there is for us no corresponding event. But if so, then neither in proclamation nor Holy Scripture has it been the Word of God that we have heard. If it had been the Word of God, not for a moment could we have looked about for God’s acts. The Word of God itself would then have been the act. The Word of God does not need to be supplemented by an act. The Word of God is itself the act of God. It is act to a degree that everything else that we usually call act, event, practice, life, etc., and that we usually miss and demand as a supplement to man’s word, can only seem to be very questionable as real act in comparison with it. The Word of God makes history in the supreme sense.
The fact that God’s Word is God’s act means first its contingent contemporaneity. What is meant by this is as follows. The time of the direct, original speech of God Himself in His revelation, the time of Jesus Christ (which was also and already that of Abraham according to Jn. 8:56), the time of that which the prophets and apostles heard so that they could bear witness to it—that is one time. But the time of this witness, the time of prophecy and the apostolate, the time of Peter on whom Christ builds His Church, the time of the rise of the Canon as a concrete counterpart in which the Church receives its norm for all times—this is another time. And the specific time of the Church itself, the time of derivative proclamation related to the words of the prophets and apostles and regulated by them—this is yet another time. These are different times distinguished not only by the difference in periods and contents, not only by the remoteness of centuries and the disparity in the men of different centuries and millennia, but distinguished by the different attitude of God to men. Jesus Christ was no less true man than the prophets and apostles. But in virtue of His unity with God He stood absolutely over against them as a master over against his slaves…It is this difference of order, of first and second, of higher and lower, that makes the times of the Word of God so different. Three times there is a saying of the Word of God through human lips. But only twice, in the biblical witnesses and us, is there first a letting of it be said to us, and only once, in our case, an indirect letting of it be said to us mediated through the Bible…
…if we abandon the distinction of the three times in terms of order, then no matter how loudly or sincerely we may talk about revelation and its concreteness and historicity, and no matter how illuminating or practical may be the shape we give everything, we have really abandoned the concept of the Word of God itself. When we are able to eliminate our non-contemporaneity with Christ and the apostles by putting ourselves on the same soil as them or putting them on the same soil as us, so that, sharing the same prophetic Spirit and having the measure of inner truth in our own feeling, we can discuss with them the gross and net value of their words; when contemporaneity, therefore, rests on the hypothesis of a merely quantitative difference between them and us, then the concept of the Word of God is humanised in such a way that it is no wonder people prefer to use it comparatively rarely and in quotation marks; the surprising thing is that they have not preferred to drop it completely and unequivocally…The present Church, however historically it may feel and think, speaks the last word as the heir and interpreter of history. Not having God’s Word in the serious sense of the term, it stands alone and is referred back to itself. If, however, we insist that the concept of God’s Word means that the Church is not alone and is not referred back to itself, then we must accept the fact that the distinction of the times is one of order, and in no case can the contemporaneity of modern proclamation with Scripture and revelation be understood as one that we can bring about by eliminating the distinction, by incorporating Scripture and revelation into the life of humanity. It can be understood only as an expression of the fact that God’s Word is itself God’s act…
The fact that God’s Word is God’s act implies secondly its power to rule. God’s speech is His action in relation to those to whom He speaks. But His action is divine. It is the action of the Lord. It is thus His ruling action. When and where Jesus Christ becomes contemporaneous through Scripture and proclamation, when and where the “God with us” is said to us by God Himself, we come under a lordship. The concepts election, revelation, separation, calling, and new birth which we touched on earlier all denote a promise, a judgment, a claim on man by which God binds man to Himself. Gospel and Law as the concrete content of God’s Word imply always a seizure of man. No matter what God’s Word says to man in concretissimo, it always tells him that he is not his own but God’s. If in the light of its origin in revelation, in Jesus Christ, we understand the Word of God as the epitome of God’s grace, grace means simply that man is no longer left to himself but is given into the hand of God…
If a man knew nothing of this power that both sustains and stimulates, both protects and punishes, both pacifies and disturbs, if he merely heard about it without knowing it as a power, he would only give evidence that he knew nothing of the Word of God. We are acquainted with the Word of God to the degree that we are acquainted with this power. We speak of God’s Word when we speak in recollection and expectation of this power, and when we do so in such a way that we realise that this power of the Word of God is not one power among others, not even among other divine powers, but the one unique divine power which comes home to us, to which we are referred, in face of which we stand in decision between the obedience we owe it and the unfathomable inconceivability of disobedience, and consequently in the decision between bliss and perdition. The Holy Spirit, at least according to the Western understanding of the divine Triunity, cannot be separated from the Word, and His power is not a power different from that of the Word but the power that lives in and by the Word. Nor do we know anything about God’s power in the creation and governance of the world except through the Word revealed, written and proclaimed. And when we know it through this Word we cannot possibly separate it from the power of the Word…
Where God has once spoken and is heard, i.e., in the Church, there is no escaping this power, no getting past it, no acknowledgment of divine powers that are not summed up in this power, that are not related to the manner of this power and active in its mode…All this must be said of the Word of God because the Word of God is Jesus Christ and because its efficacy is not distinct from the lordship of Jesus Christ. He who hears God’s Word is drawn thereby into the sphere of the real power of this lordship. There applies to him and for him everything the Word of God says as promise, claim, judgment and blessing. Preaching does not put it into effect; preaching declares and confirms that it is in effect. It is proclamation of the Word of God when it proclaims it as something that is already in effect.
That Barth is correct in his assertion that the Word of God is the Act of God, that God’s speech is his action in revealing himself and ruling his creation, is evident throughout Scripture: “…so shall my word be that goes from my mouth; it shall not return to me empty, but it shall accomplish that which I purpose…” (Is. 55:11). This means, then, that to hear the Word of God is to be claimed, acted upon, and ruled by God himself: “at the name of Jesus every knee should bow…and every tongue confess that Jesus Christ is Lord” (Phil. 2:10-11). It is possible, of course, for us to mishear the Word of God, or to understand but reject and disobey it, but this is only possible because the Word has first sovereignly claimed us in being spoken to us. It is the effectual action of the Word on us that makes us responsible to respond rightly and inexcusable if we respond wrongly.
This means that, in the final analysis, it is not upon our interpretation (or misinterpretation!) that the efficacy of the Word depends. Neither is it the antiquity of our ecclesial tradition or the validity of our orders of ministry that guarantee that the Word of God will not return empty but will accomplish its divine purpose. No, it is because the Word of God is ultimately the act of God — the divine speech that “calls into existence the things that do not exist” (Rom. 4:17) and that reconciles as it reveals —that the Word is sure to evade any human attempt to domesticate it or overrule any human misuse of it and infallibly accomplish its end: creating light out of darkness (Gen. 1:3), breaking through rock like a hammer (Jer. 23:29), and raising the dead to life (Ezek. 27:4-5).
It is because the Word of God is not dead and mute but living, active, and seated on the throne of heaven from whence he pours out his “Spirit of truth” to “take what is mine and declare it to you” (John 16:14) that ensures the Word’s “contemporaneity” with us and over us even now in our present time. Therefore, the Word of God is, as Barth recognized, something that the church can speak to itself and to the world only after it has first been spoken to the church. Only if it were possible for us to erase the “non-contemporaneity” of the Word in its continual and direct address to us could we then suppose that our own words, however important or authoritative, assist, supplement, substitute, or exist alongside of that one Word which is the same yesterday, today, and forever. Yet if this were possible, then the Word of God would not longer be the Word of God but a mere human word, and would be thus emptied of its divine power and efficacy.
If we carry this understanding of the Word of God consistently through to its theo-logical end, we will be left with only one conclusion, the one that Karl Barth clearly expressed in this context:
[And he is the head of the body, the church] (Col. 1:18, cf. Eph. 1:22f.). This is said of Christ. But Christ is the Word of God, contemporary in prophecy and the apostolate and contemporary in the proclamation of His Church. If He is contemporary here, if He makes that step, then we are necessarily faced with the recognition of the sovereignty of God’s Word in the Church which characterises the Reformation view of God and the Church.
This, in short, is the reason for sola Scriptura.
 Karl Barth, Church dogmatics I/1 (London; New York: T&T Clark, 2004), pp.143-5, 147-150, 153. Emphasis mine.
 Ibid., pp.150-1.