The apartment is in an old and deteriorating building in what is probably a low-rent neighborhood. The owner does not want to spend a lot of money on it because he expects to tear it down to make way for a much larger building. The condition of the sticking windows suggests the general condition of the apartment and the pld-fashioned brick building. It represents Tom and Clare's income and social status and what he would like to get away from.
Most of the putty, dried out and brittle, had dropped off the bottom edging of the window frame...
This window will give him all kinds of trouble in the story. It slams shut when he wants it open and won't open when he wants to climb back inside.
Tom's wife probably works as a secretary. He would like to have children and a home in the suburbs, a new car for himself and another for Clare, who could stay at home or play tennis at the country club while the maid looked after the children.
Surrounded by signs of wealth in a city like New York, deluged with advertising of consumer goods by the newspapers, magaines, and the new medium of television, it is easy for a smart young married man to want better things and to undervalue what he has already got.
All human situations have their inconveniences. We feel those of the present but neither see nor feel those of the future; and hence we often make troublesome changes without amendment, and frequently for the worse.
Tom has his youth, health, intelligence, and a beautiful and loving wife. He lives in a city that offers unlimited cultural and educational amenities--and yet he can't even take time off to go to the movies with his wife.
Once he is out on that ledge and feels certain he is going to fall to his death, he realizes how happy he had been in that modest apartment, because it was a home, a bright, warm haven in a cold, heartless, ruthless city--the city he had just had a good look at when he was standing out on that ledge. He also realizes that, even if he could succeed in getting back inside his apartment, he is still in danger of losing his wife, who couldn't be expected to put up with his neglect forever.
Dropping his palms to the sill, he stared into his living room--at the red-brown davenport across the room, and a magazine he had left there; at the pictures on the walls and the gray rug; the entrance to the hallway; and at his papers, typewriter, and desk, not two feet from his nose. A movement from his desk caught his eye and he saw that it was a thin curl of blue smoke; his cigarette, the ash long, was still burning in the ash tray where he'd left it--this was past all belief--only a few minutes before.
The experience on the ledge was a nightmare, but it was the best thing that ever happened to Tom. It made him open his eyes and see the truth. Life is short and fragile. Love is precious. Hubris is suicidal.