The Birth of Tragedy by Friedrich Nietzsche

In The Birth of Tragedy Nietzsche begins with a simple postulate: Why do we enjoy watching tragedies?  The Greeks loved drama that emphasized the profound nature of suffering in the world and they weren't particularly dour or unproductive people.  Instead, Nietzsche tells us, tragedy has a way of allowing us to face suffering without breaking, of wresting a strange sort of consolation from seeing pain enacted on stage.

This process is based on two forces, which Nietzsche names after the respective gods which represent them, the Apolline and Dionysiac.  The Apolline force is beauty, order, representation; it belongs to sculpture which is beautiful because it faithfully represents (to the best of its ability) recognizable forms.  The Dionysiac form is the sublime, dark, mysterious, closer to the "real;" it belongs to music, the wordless expression of the will.  These forces are not necessarily at odds with one another, in fact, true tragedy (which for the Greeks was always musical) comes from the combination of these two forces.  To describe it reductively, the deceptive nature of the Apolline allows us to approach the terrifying nature of the Dionysiac without self-destruction:

However powerfully this pity may affect us, in a sense it delivers us from the primal suffering of the world, just as the symbol of myth preserves us from gazing directly on the supreme idea of the world, just as thoughts and words save us from the unbrooked effusion of the unconscious will.

Nietzsche follows this idea off to several conclusions, including heaps of praise for Richard Wagner and scorn for Euripides and Socrates, as well as the concept of reason itself.  His most powerful conclusion is that "[t]he world is only justified as an aesthetic phenomenon," something which, if too strong for that word "only," nonetheless squares with my personal experience of the power of art--that it is, among other things, the force that makes life endurable.