Part IV Summary

Get out the microscope, because we’re going through this poem line-by-line.

OK, so Coleridge isn't super-obvious about it, but at this point the Wedding Guest (remember him?) interrupts the story to make another futile attempt at escape.
After the Mariner tells this ghost story, the Wedding Guest notices that the Mariner looks a bit like a ghost himself: skinny, bony, with eerily bright eyes. Yup, all ghost-like features. Putting two and two together, the Wedding Guest freaks out.
But the Mariner reassures him that he's no ghost. He was the only one on the ship who didn't die. He doesn't exactly give the Wedding Guest a lot of comfort, but just goes on with his story.
The Mariner's story continues:
So now he's by himself on this ship with a lot of dead people, all of whom have just cursed him. He wishes that the spirit of some dead saint would take pity on him.
At least the slimy creatures are still there. He thinks what a shame it is that all these nice men have died, and he and the slimy things are still living.

He tries to say a prayer to save his soul, but then he hears an evil voice like a little devil on his shoulder that saps his enthusiasm for praying.
He closes his eyes to avoid looking at all the miserable sights around him. He has noticed that the bodies of all the dead sailors don't rot. Also, they're still cursing him with their looks. Let it go, guys.
Their curses are worse than the curse of a poor little orphan. And that's really bad, because an orphan could drag an angel down to Hell. For a full week, the eyes of the dead sailors emanate this terrible curse.

At night, the moon rises again, and the moonlight falls on the ship like frost.
He still sees all kinds of strange bright colors, like a red on the water, and a bright, "elfish" white light in the trail of the water snakes.
Wait, when were there water snakes? Oh, yeah, the "slimy things." Wait, we thought those had legs. OK, just go with it.
He looks at the water snakes swimming in the shadow of his ship. It's like a creepy version of Dr. Seuss: One Snake, Two Snake, Red Snake, Blue Snake. They are all different colors, and they make crazy phosphorescent patterns in the water.
He kind of gets excited watching the snakes. Look at the colors! He realizes that these hideous snakes are kind of beautiful. Without knowing it, he blesses the wriggly little creatures in his heart.
This blessing for fellow creatures is all it takes to remove the horrible curse that the Mariner gained from killing the albatross. He has been wearing that darn albatross around his neck this whole time, but suddenly it falls off and sinks to the bottom of the ocean.
He can pray again without being stopped by evil whispers. As Martha Stewart would say, "It's a good thing."