Many people are critical of Karl Barth’s insistence on not simply a Christocentric approach to biblical interpretation and theology (something that, as Richard Muller has shown, is pervasive in the Reformed tradition) but a Christo-constricted approach. That is, instead of simply thinking of Christ as the goal (the Christocentric approach), a Christo-constricted approach looks to Christ alone (solus Christus!) as the singularly determinative factor that limits and guides the entire process of interpretation and theology from start to finish, much like the banks of a river limit and guide the water to its proper destination. In this way, a Christ0-constricted approach gives a distinctly Christological shape not merely to Christology but to every aspect of faith and practice.
Now the reason why many people are critical of Barth on this point is precisely because it seems too, for lack of a better term, constricted. That is to say, it appears to impose an arbitrary principle that can distort the interpretation of biblical texts or other doctrinal loci by forcing them to conform to an artificial framework. For his part, however, Barth argues the exact opposite; for Barth, it is the non Christo-constricted (even Christocentric) approach that opens the door to any number of interpretive and theological problems. Barth writes:
Our crucial first statement, “that the eternal Word of God chose, sanctified and assumed human nature and existence into oneness with Himself, in order thus, as very God and very man, to become the Word of reconciliation spoken by God to man,” signifies the mystery of the revelation of God in Jesus Christ. That is to say, in this statement we describe absolutely the sole point in which New Testament witness originates, and therefore, also, the sole point from which a doctrine of revelation congruous with this witness can originate. We do not look for some higher vantage point from which our statement can derive its meaning, but we start from this point itself. This, of course, we cannot do by our own authority and discretion. We can only make it clear from the Evangelists and apostles what it will mean to start from this point, and then try to make clear what our own starting-point is. But we cannot get “behind” this point. Therefore we cannot derive or prove the statement, in which this point is to be described, from a higher discernment. We can only describe it as a starting-point. Whatever we think or say about it can only be with the aim of describing it again and again as a mystery, i.e., as a starting-point.
If revelation is to be taken seriously as the revelation of God, and not just as an emphatic expression for a discovery which man has made in himself or in his cosmos by his own powers, then in any doctrine of revelation we must deal expressly with the point that constitutes the mystery of revelation, the starting-point of all thought and language about it. At all costs we must make it clear that an ultimate mystery is involved here. It can be contemplated, acknowledged, worshipped and confessed as such, but it cannot be solved, or transformed into a non-mystery. Upon no consideration must it be treated in such a way that the mystery is resolved away. In Christology the limits as well as the goal must be fixed as they are seen to be fixed already in the Evangelists and apostles themselves; i.e., the goal of thought and language must be determined entirely by the unique object in question. But this same object in its uniqueness must also signify for us the boundary beyond which we are not to think or speak. Christology has to consider and to state who Jesus Christ is, who in revelation exercises God’s power over man. But it must avoid doing so in such a way as to presuppose that man may now exercise a power over God. It must state definitely what cannot be stated definitely enough. But even so it must observe its own limits, i.e. the limits of man who has seriously to do with God’s revelation.
Essentially Barth is saying here that far from being an arbitrary or artificial imposition on Scripture, it is Scripture itself which directs us to Christ as the boundary line beyond which we must not cross at any point in our interpretation or theologizing. When we pay close attention to the witness of the New Testament authors, we discover how relentlessly they pointed away from themselves and to Christ as the Word of God enfleshed, as the ultimate and definitive revelation of God to which the law and the prophets were only pointers, as the substance in whose light everything else becomes shadow:
Long ago, at many times and in many ways, God spoke to our fathers by the prophets, but in these last days he has spoken to us by his Son, whom he appointed the heir of all things, through whom also he created the world. He is the radiance of the glory of God and the exact imprint of his nature, and he upholds the universe by the word of his power. (Heb. 1:1-3)
Never in Scripture do we find the authoritative witnesses trying to, as Barth says, “get behind” that which God has spoken in Christ who, as the radiance of God’s glory and the exact imprint of his nature, does not merely reveal things about God but reveals God himself in his very own incarnate person. Even to attempt to get behind Christ for another revelation, for another word from God, for something higher and greater, for some principle or system or method, is to insist on going the way that God’s revelation has prohibited to us and trespass on ground that even angels fear to tread. In other words, a Christo-constricted approach to interpretation and theology is not arbitrary or artificial imposition, but the only path left to those who wish to repentantly submit all their thought and speech about God to the actual way he has taken in revealing himself to us in Christ. In Christ, God has clearly established the limits that hedge us in on every side, the boundaries that dictate the way we must take in seeking knowledge of him. Were we to assert our independence by pursuing a knowledge of God outside of these Christological confines, we would be doing nothing less than trying to assert ourselves against God himself. Thus, a Christo-constricted approach is, in the final analysis, simply a matter of obedience.
 Barth, K., Bromiley, G.W. & Torrance, T.F., 2004. Church dogmatics: The doctrine of the Word of God, Part 2, London; New York: T&T Clark. pp.124-125