An imperative, "you - shine like stars" or a nominative, "you shine like stars"? I'm going with nominative, and not checking the Greek for the verse in Philippians.
Today we talked about stars, how God knows and names them, how God ensures not one is missing, and how we are likewise loved and cherished. And we learned of a star named for our church, in the 'Arrow' constellation, which shines in the night sky, even if we cannot see it.
You shine - it's a fact, a thing, a truth... even if sometimes the light is dimmed or hidden, it's still there. God sees it and God knows it.