They never precisely say what role Lumiere serves in the Beast's castle—besides sentient light source, that is—but we're gonna go with butler. In this case, that means he's the guy who oversees the dining room, wine cellar, and kitchen.
Oh, he's also a candelabra.
In fact, we'd say he's primarily a candelabra, with the butlering thing coming second to providing warm and reliable illumination.
"Warm" is actually a good way to describe Lumiere's personality. He's a natural servant: eager to help other people be comfortable and ready to offer them anything they might need. The whole story kicks off because he offers Maurice shelter from the super scary wolves in the forest ("I was trying to be hospitable!" he explains to an incensed Cogsworth), and he later convinces the Beast to let Belle stay in a nice room instead of that manky old tower. Other people come first for Lumiere, and he takes pride in his ability to make folks comfortable.
He even has a song about it, which, if we can rave, brings down the house.
Here's the thing: Lumiere is a victim of the Beast's curse since he clearly didn't do anything to merit being turned into a knickknack. But, he doesn't let it get him down, either. He's friendly and inviting, with a little spring in his ornate bronze step and a smile for everyone he meets. Oh, yeah, and lest we forget, he's got grabby hands, too…though at least he doesn't play the field, focusing instead on that fetching little feather duster who seems happy to play moth to his sizzling flame. (Did you see the look she gave him at the wedding at the end? Come on, guys, this is a Disney flick!)
Eh, what are ya gonna do? They're French.
Bottom line: Lumiere adores his fellow man, has a zesty lust for life, and lives to make other people happy.
Explain to us again why he's not the hero in this one?