Harrison argues that the narrative, or a narrative, of the Symposium is Socrates’s triumph over Dionysus. 

The Symposium takes place at a Dionysian celebration of a Dionysian celebration, an after-party of the tragic festival. 

Here Socrates shows himself unaffected by wine, rebuffs and baffles (while entrancing) Alcibiades who comes from without in the form of the god.  Alcibiades/Dionysus presumes to act as the judge of the speech contest and crowns Socrates alongside Agathon, but Socrates lies beyond the one who judges.  Think how Alcibiades cannot grasp what Socrates is all about, cannot understand him, is intoxicated by him.  We might compare Christ before Pilate. 

Dionysus cannot affect Socrates because he is inebriated already, by the Good.  And, ending the night by arguing tragedy, with guests half-lulled to sleep by the god he vanquished, he emerges into the dawning light of Apollo’s day.