Why does the Mariner stop that particular wedding guest?Of the one in three why was he selected?

In Coleridge's "The Rime of the Ancient Mariner," the
Mariner has no choice but to tell his tale to the wedding guest that he tells the tale
to.  The Mariner reveals to the guest:

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"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. 
(582-590)

The Mariner just
knows, and is in fact forced by the curse to tell his tale to that particular wedding
guest. 

No information is revealed as to why this
particular listener is "chosen" by the curse, he just is.  In a poem within which
rational thought and linear development is replaced with the imagination and the
supernatural, this shouldn't come as a surprise.  Rational explanations are not required
in a work of imagination.