"It is an ancient Mariner, And he stoppeth one of three. 'By thy long grey beard and glittering eye, Now wherefore stopp'st thou me?'"
I have only one minor issue with this question, and it's this: it seems to me that the three men are not on their way to a wedding. They're going to the feast, which suggests – to me, at least – that the wedding itself has already taken place.
"The Bridegroom's doors are opened wide ... The guests are met, the feast is set: May'st hear the merry din.'"
"Unhand me, grey–beard loon!" cries the unfortunate Wedding–Guest – next of kin to the bridegroom, no less. But the Mariner "holds him with his skinny hand" and the unfortunate wedding guest is forced to listen to his sorry tale.
When the grisly tale is told, the Guest is so disturbed by it that he "Turned from the bridegroom's door. He went like one that hath been stunned, And is of sense forlorn: A sadder and a wiser man, He rose the morrow morn."
Not from the church door, but from the bridegroom's door. So at least (if my interpretation is correct) he got to see the happy couple exchange their vows.
Actually, on reflection, I have another minor issue: I don't think we're ever told that the three guests are all men. It might be a man and two women. Or even a man, a woman and a child.
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