Michael Reeves, writing about Karl Barth’s loquaciousness in his new book: Theologians You Should Know: An Introduction: From the Apostolic Fathers to the 21st Century (Crossway, 2016), page 280:
Barth believed that the task of theology is the same as the task of preaching, and thus preaching is just what he does in the Church Dogmatics. But preaching is not about merely conferring information: it is about winning hearts, and thus involves the sorts of persuasion and repetition that take time. Points must be reinforced, the readers won. The result is that Barth can be deeply moving to read. It also means he is peculiarly resistant to being quoted. Context is needed, and this is why, when he is quoted, he usually sounds impossibly complicated and so off-putting. Perhaps most important of all, though, the fact that Barth writes in such a sermonic, almost story-telling style actually means the reader can relax. Failing fully to grasp a few pages really will not matter, for the sweep of the argument is larger than that.
Looking for the bigger picture is the main thing. Colin Gunton put it like this:
Barth is an aesthetic theologian. Barth worshiped before he theologized. His love for Mozart is to be noted here. The structure of Barth’s theology is assertive, it is not argumentative; it can be considered as a sort of music. In the sense that Barth is not concerned to argue any more than Mozart is concerned to argue, Mozart just plays. I think that is Barth’s aim: to play on the revelation of God so that its truth and beauty will shine.
Of course, that does all mean that Barth demands you give him time. He will not dish out theological fast food. But giving him time does make one a more thoughtful theologian.