For Barth the three-fold Word - Christ, Scripture and Proclamation - means that preaching should always be Scriptural and always witness to Christ. Here he makes it clear that christo-centrism is not something the preacher (or the biblical theologian) bestows on the Bible. Rather, the Bible is already and inherently witness to Christ:
"The Bible says all sorts of things, certainly; but in all this multiplicity and variety, it says in truth only one thing - just this: the name of Jesus Christ... The Bible becomes clear when it is clear that is says this one thing... The Bible remains dark to us if we do not hear in it this sovereign name... Interpretation stands in the service of the clarity which the Bible as God's Word makes for itself; and we can properly interpret the Bible, in whole or part, only when we perceive and show that what it says is said from the point of view of that... name of Jesus Christ." (I/2, p720)
What about the Old Testament? For Barth...
"the Old Testament is witness to Christ, before Christ but not without Christ... As a wholly Jewish book, the Old Testament is a pointer to Christ." (Homiletics, p80)
Barth does not consider the christo-centric meaning to be a sensus plenior in addition to the literal sense.
"the natural sense is the issue... [we do not] give the passage a second sense... This passage in its immanence points beyond itself... The Old Testament points forward, the New Testament points backward, and both point to Christ." Homiletics, p80-81.
As for the New Testament, Barth insists that christocentric preaching is no less important here.
"One can never say of a single part of the narrative, doctrine and proclamation of the New Testament, that in itself it is original or important or the object of the witness intended. Neither the ethics of the Sermon on the Mount nor the eschatology of Mk 13 and parallels, nor the healing of the blind, lame and possessed, nor the battle with the Pharisees and the Cleansing of the Temple, nor the statements of the Pauline and Johannine metaphysics and mysticism (so far as there are any), nor love to God nor love to neighbour, nor the passion and death of Christ, nor the miraculous raising from the dead - nothing of all that has any value, inner importance or abstract significance of its own in the New Testament, apart from Jesus Christ being the subject of it all. His is the name in which it is all true and real, living and moving, by which, therefore, everything must be attested." I/2, p10-11
This is a helpful reminder. We usually hear from the Old Testament sermon some "bridge to Christ" (however tenuous!). Yet what does it say when the same preacher can manage to preach Christlessly from the New?
Do preachers really believe that the Scriptures are already Christ-focused? Or is it our job to add a second layer of Christ-centredness? If a preacher breathes a sigh of relief once they're in New Testament waters, and if they then fail to witness to Christ while there - what does it say about their view of the Old and New Testaments?
Barth is really helpful here. Scripture exists within the perichoresis of the three-fold Word. It exists to be preached. And it exists (every part of it) as witness to Christ. It is not the preacher's job to make it into a witness to Christ. If we find our Old Testament sermons involve some weird change of gears in order to 'get to Christ', we've not understood the bible properly. If we find that our New Testament sermons fail to point people to Christ, we've not understood the bible properly. These issues might be a sign you've bought into the wrong biblical theology.
Just a thought.
Here's my length paper on Barth and Preaching.