Ladies and gents, you are here assembled
To hear why earth and heaven trembled
Because of the black and sinister arts
Of an Irish writer in foreign parts.
Joyce sets the stage for his poem as an assembly, which indicates that he is going to put on some sort of show before the crowd. 
 Posturing is a very familiar thing to Joyce, for instance, during a performance of ‘'William Tell’‘ by an Irish tenor who was his protege, he put on enough of a one-man ovati on–dramatized by the front-row spectacle he made with his cape and white cane–to get two encores.
Gas from a Burner