Why do Mokichi, Ichizo and Kichijiro have to leave the village?

The guards demand that the peasants admit to their Christian faith or the guards will take a hostage. The Jiisama makes an unsatisfactory reply and is promptly taken away. Three days later an elderly samurai returns to the village and again demands that the people confess their religion. If they refuse, the peasants have to pick a hostage. It is decided that Mokichi, Ichizo, and Kichijiro will present themselves before a magistrate.