The Ball and the Cross by G.K. Chesterton

THE BALL AND THE CROSS is a tale of two men, one an atheist, the other a Catholic, who want to fight a duel over God and the Virgin Mary. The world thinks them both mad, of course, because they seem to be serious, and the story ends by shutting up in a lunatic asylum all the people who are sane enough to care one way or another about their quarrel.