The mariner felt that it was cursed, and that by shooting it, the crew's luck would change. I saw a movie or something recently which reminded me of the poem, but I can't remember what it was. It wasn't based on the book.

and was treated as a good luck charm, but then the wind died. The Mariner killed it out of scorn for the earlier mistaken belief. He didn't understand that it wasn't the albatross' blessing for good wind or fault for bad wind, but that the bird was just another innocent creature on this planet doing what we do. He killed the bird because he transferred his anger at belief on the bird itself. And of his shipmates, some thought it was wrong to kill the bird who brought the fair wind, and there were others who claimed it brought the rain and fog.

Their argument didn't matter because they all dropped like flies. The mariner survived largely to get his particular epiphany--

Being so alone that only the sight of water snakes as fellow living things made him cherish them, the albatross curse fell off. He now understood himself as a part of the natural world, and recognizes the preciousness of all life.

A rain fall, baptizing the ships deck, and the "dead" arise. So who knows if the epiphany was even real. He talks of being in a fever--maybe this perspective is part of a fever dream?

What does it all mean? I dunno. Except for Byron and sometimes Shelley, I can't read the Romantics without wishing they'd wind it the heck up before they lapse into nice-sounding but otherwise useless doggerel. And none of this necessarily explains why people are being so solicitous of a raving codger when they are trying to get a wedding on, over here. 'Cause really. Here's a couple pound notes, get off with ye, I am in the middle of an important life-event.