Keats's "Bright Star" gives us the perspective of somebody on earth looking up at a single, extremely special star in the heavens. This is the North Star, the one star that stays fixed in its place for all time. All the other stars on the sky are constantly changing positions as time passes: they all rotate around the North Star. And the same goes for life on earth: the waters come and go, the seasons come and go, snow falls, and generations are born and die. But the speaker doesn't want to be like the star way up there in the heavens. He wants to take that same eternal existence of the star and enjoy it on earth, in the company of the woman he loves. He loves the things that won't last forever. But that won't stop him from wanting them to last forever.
Everything in the poem that moves but is also eternal has one thing in common: they all follow a cyclical pattern.
At several points in the poem, Keats uses repetition to suggest the passage of time.