A single-minded religious horror movie that strains to be shocking but refuses to offend, Scott Beck and Bryan Woods’ “Heretic” leaves itself with no other option but to have some cheeky fun at God’s expense. That proves easy enough for this chatty little chamber piece, as one of the story’s three main roles is a sadistic theologian played by Hugh Grant, who’s having the time of his life in a spirited performance that feels like a cross between “Paddington 2” baddie Phoenix Buchanan and real-world nuisance Bill Maher. “Heretic” may not be serious-minded enough to shake (or reaffirm) anyone’s faith, but it’s rare to experience a sermon of any kind delivered with such panache — and not only because Grant’s character sings Radiohead and impersonates Jar Jar Binks as part of his effort to prove that all of the world’s religions have gotten it wrong.