Final answer:
The simile 'a bright girdle furled' in Matthew Arnold's 'Dover Beach' symbolizes the once full and vibrant presence of faith around the earth, which has now receded, leaving a sense of melancholy.
Step-by-step explanation:
In the poem Dover Beach by Matthew Arnold, the simile 'a bright girdle furled' refers to the 'sea of faith' which at one point, surrounded the earth with a full and vibrant presence, similar to how a brightly lit girdle might encircle and highlight the waist. This metaphor implies that faith was once a unifying force, rich and enlivening, but has since diminished, leaving behind a sense of loss and melancholy as it withdraws with a 'melancholy, long, withdrawing roar.'