Most of the chapter's light world levels are named after terms and names in Christianity, such as Evangel, Heretic, 10 Horns, King Carrion, etc. hence the world's name, Rapture.
It Ends (the PC/Xbox Light World theme) is a remix of the original Hell theme from the Meat Boy Flash game.
You could say the chapter’s title is ironic as the word ‘rapture’ can also mean extreme pleasure, excitement or happiness, while the chapter takes place in a post-apocalyptic city.
If you pay attention to the towers in the background of level 1, you can see they are very close. However, if you look at them again in level 20, you can see they are very far away. This indicates that Meat Boy is leaving the city or moving away from the epicenter of the explosion.