Optimistic dialectic drives music out of tragedy with the scourge of its syllogisms: that is, it destroys the essence of tragedy, which can be interpreted only as a manifestation and illustration of Dionysian states, as the visible symbolizing of music, as the dream-world of Dionysian ecstasy.
This quote from Chapter Fourteen is an example of Nietzsche's continuous emphasis on the importance of music in tragedy. Music is the medium through which the Dionysian essence reaches the aesthetic man, who therefore becomes the "aesthetic listener." It is the only one of the arts to have direct access to the universal will, without requiring the mediation of some illusionary image. Music is the universal language, and it is through music that the universal force speaks. Music has the capacity to give birth to myth, and to give deep significance to Apollonian appearances. Nietzsche regards music with the highest reverence.
No wonder, then, that Nietzsche rebels so furiously against optimistic dialectic, which seeks to drive music from the stage altogether. Nietzsche makes it clear that the theoretical man has no time for mystical unions with the Primal Unity. He is on a quest for knowledge, and anything that cannot be understood by the intellect is to be cast aside as unworthy of aesthetic attention. But, in casting music aside, Socratic culture dooms itself to a superficial quest for truth according to human conceptual frameworks. The optimistic dialectic does not possess the Dionysian power of self-renewal, and thus it is doomed to exhaust itself. Until that day comes, however, the optimistic dialectic holds sway over culture, ensuring that Dionysian music remains in exile.