AFTER YEARS OF KNOCKING AROUND the Promised Land with the children of Israel, Moses already had problems enough on his hands when some of his own people, led by a man named Korah, challenged his religious authority. "What makes you and your brother think you've got a corner on holiness?" Korah said and then added, "We're all holy, every last one of us." Moses was so undone by these remarks that, as the narrator reports, "he fell on his face" (Numbers 16:4).
He eventually picked himself up, however, and asked God to help him take care of these troublemakers. God obliged by causing the ground to open up beneath their feet. Korah and his crowd were swallowed up and taken down alive to Sheol, the abode of the dead, and Moses was able to get on with the business of leading the way to the Promised Land.
You can't blame Moses for having overreacted the way he did. Leading the Israelites anywhere was no pushover, and he needed all the unchallenged authority he could get. On the other hand, you can't really blame Korah either, who, by insisting that nobody was any holier than anybody else, was simply anticipating by a few thousand years the doctrine of the priesthood of all believers.
As for God, there seems to be a strong possibility that the reason he caused the rebels to be swallowed down into Sheol alive was so that later on, when the whole thing had blown over, he could let them out again quietly through the back door.