At the end of Gremlins, Gizmo, if he could talk, would say, "Let there be light." He opens some blinds, shining sunlight on Stripe and melting him into a goopy puddle. With the last of the gremlins dead, Kingston Falls is back to square one, with a slightly smaller population than it had on Christmas Eve.
Billy and his fam recuperate at home when they get a special visitor: Grandfather. He's come to take Gizmo back to China town. But first, he lectures the Peltzers for abusing their mogwai privileges.
GRANDPA: You do with Mogwai what your society has done with all of nature's gifts. You do not understand. You are not ready.
One way to interpret is speech is to picture Grandfather as the Lorax climbed down off his "UNLESS" rock. He appears to be criticizing Billy for not respecting the environment.
But that doesn't make sense because Gremlins has no other environmental message. So what does Grandfather mean?
Consider this: one of the first things Grandfather does upon entering the Peltzer home is express disapproval over Gizmo's watching TV.
And overarching theme in Gremlins is a fear of the unknown. By bringing Gizmo into his home, Billy's Americanized him. Gizmo now sits on his butt and watches TV. That isn't much different than sitting in a cage and not watching TV, which is what he did in Grandfather's shop, but Grandfather still disapproves.
Perhaps the residents of Kingston Falls aren't the only ones who fear change.