David Bentley Hart writes:
Bach is the greatest of Christian theologians, the most inspired witness to the ordo amoris in the fabric of being; not only is no other composer capable of more freely developing lines or of more elaborate structures of tonal mediation (wheresoever the line goes, Bach is there also), but no one as compellingly demonstrates that the infinite is beauty and that beauty is infinite. It is in Bach's music, as nowhere else, that the potential boundlessness of thematic development becomes manifest: how a them can unfold inexorably through difference, while remaining continuous in each moment of repetition, upon a potentially infinite surface of varied repetition. p. 282-3
Choosing Bach of course presents Hart with fewer difficulties than Barth's choosing of Mozart: Barth had to admit that Mozart was not a good man, and probably not a very firm believer. So, he had to seperate the music from the man. Here, no such problem: the composer could not, would not have composed as he did apart from the knowledge of God that he clearly had.
I find it interesting that Hart the Eastern Orthodox exults Bach the Protestant when Hart is so anti-Protestant in general. And yet there is a Protestant plainness to Bach, even when he is writing music for Masses. This aesthetic, far from being evidence of a dour disposition, is I think one of Protestantisms great strength: it is in better taste than the alternatives within Christianity (think the saccharine ornateness of much Catholic and Orthodox art...). At least, that is a Hartian argument!
