The Ancient Mariner tells the wedding guest in the final stanza of the first part of the poem of his thoughtless act which has such cataclysmic and bizarre consequences for him and the rest of the crew-
God save thee, ancient Mariner!
From the fiends, that plague thee thus!—
Why look'st thou so?”—With my cross-bow
I shot the Albatross!
The mariner then tells that he is punished by the rest of the crew for his mean and portentious act.
And I had done an hellish thing,
And it would work 'em woe:
For all averred, I had killed the bird
That made the breeze to blow
In a bid to assuage the evil spirit which the crew believe is now plaguing the boat, the mariner is made to bear the burden of the killing of the albatross alone -
Ah! well a-day! what evil looks
Had I from old and young!
Instead of the Cross, the Albatross
About my neck was hung.