"...all the world had become Cordelia Street"
The world on Cordelia Street represents for many the attainment of the American Dream. Situated in a respectable part of town where folk sit on the porch on Sundays to gab with their neighbors while children play in the street. Far away from tenements and slums, Cordelia Street represents a step up the middle class ladder of success that says something. To Paul, of course, Cordelia Street represents the exact same thing…except it is a nightmare rather than a dream. In the darkest depths of his depressed state, there is no escape from such a nightmare; it is everywhere.
"he breathed like a prisoner set free"
The point of comparison to this simile is that the world represents a prison to Paul and the doors to Carnegie Hall are like the prison walls he must tunnel through in order to feel free and alive again.
"The Park itself was a wonderful stage winter-piece."
Entry to his escape from reality inside the theater denied him, Paul withdraws further and further into his own make-believe world. As he draws closer and closer to suicidal madness, even the real world starts to seem like components of a fictional representation. The winter wonderland of Central Park becomes unreal for him, transforming into metaphorical set design.
"There it was, what he wanted—tangibly before him, like the fairy world of a Christmas pantomime"
What he wants is itself a metaphor since the simile here is comparing the Schenley Hotel—where all the artists who come to town to perform take their lodging—to a fairy world. The Schenley is not what Paul want, it is merely a tangible metaphor for everything romantic and aesthetic; a place where people with talent—rather than mere ability—are treated like the special cases they are. The double use of figurative language here transforms Paul’s want—to be treated as the special case he is—creates another doubling: the world he dreams of is not one occupied by actual fairies, but an artistic rendering of a fairy world, thus reinforcing the motif of Paul’s world always being one step removed from reality, even when the reality is mythical.
"and Paul dropped back into the immense design of things."
These are the final words of the story, presenting a horrifying reversal of fortune for Paul. Death—the abyss, the void, the Big Sleep—is here presented in the form a metaphor coincident with the very Calvinist theoretical concepts of predetermination and predestination that Paul struggles desperately to disprove. The metaphor suggests with powerfully tragic strength that every single action undertaken by Paul to escape this predestined fate was, in fact, inscribed into his future at the moment of his birth.
