In Coleridge's The Rime of the Ancient Mariner, the mariner is cursed because he has killed the albatross, showing a criminal disregard for a creature of nature. Everyone on the ship is cursed (the mariner because he killed the bird—and the crew that eventually condoned his action). Their sentence is death.
However, the supernatural Death and Life-in-Death gamble for the lives of the sailors. Death wins all the lives of the sailors except for the mariner's. The mariner's fate is sealed at this moment.
One of the mariner's actions shows he has been forgiven to an extent: when he praises the beauty of the creatures in the ocean, the albatross (which had been tied by the sailors around his neck) falls off, into the sea. A spirit also speaks of the mariner's punishment:
The other was a softer voice,
As soft as honey-dew:
Quoth he, “The man hath penance done,
And penance more will do.” (403-406)
Saved from death, the mariner watches the ship sink and is saved by a small boat. Reaching land, and at his request, he is further forgiven of his sins by confessing to a Hermit (a holy man); it is in the telling of his story that the mariner realizes that while forgiven, he must still suffer the consequences of his actions—through a recurring pain—in order to atone for what he has done.
Since then, at an uncertain hour,
That agony returns;
And till my ghastly tale is told,
This heart within me burns.
I pass, like night, from land to land;
I have strange power of speech;
That moment that his face I see,
I know the man that must hear me:
To him my tale I teach. (575-587)
The mariner is forced (physically compelled) to travel and tell his tale. He knows as soon as he meets someone if that person needs to hear what the mariner has to say—and he has also been blessed with a strange eloquence—a captivating "power of speech." The mariner's heart burns within his chest until he shares his experiences. It is only then that he is released from this "cursed state," and only until it is time to tell the tale again.
This is what he has now done in telling the Wedding Guest his story. In this way, the message to mankind—to respect nature—is passed along (in this epic poem) by the mariner.