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?
Why it works
These opening lines immediately establish the hallmarks of narrative poetry: a named character (the ancient Mariner), a specific action (stopping one of three wedding guests), and an inciting dramatic encounter complete with dialogue — all of which launch the story's forward momentum from the very first stanza.