what occasion does the mariner tell his story, and why would Coleridge chose this occasion for the poem?

In the poem's first line, we meet its protagonist, "an ancient Mariner." He stops one of three people on their way to a wedding celebration. The leader of the group, the Wedding Guest, tries to resist being stopped by the strange old man with the "long grey beard and glittering eye."

We can infer that there's something special about bothh the Mariner and his tale. The choice of the wedding guest, who becomes so mesmerized that he cannot pull himself away from the tale, speaks to fascinating details.

The poet deliberately chooses the occasion of a wedding ceremony for the ancient mariner to narrate his devastating tale.The mariner,by now had totally abstained from worldly pleasures and was leading a miserable life,unable to even control his instincts.The wedding guest,on the contrary was the exact opposite.He yearns to join his friends in a social and merry setting, full of decadent pleasures such as fine food, wine, song, and dance. A marriage essentially signifies an extravagant atmosphere and is symbolic of the worldly pleasures.This could be the reason why the poet chose this occasion.