Moses brought the Israelites to a place called Meribah. They couldn’t find any water to drink there, because it was a desert, so they complained to Moses. The Israelites had been in the same situation here in Meribah before, and God had told Moses to hit a rock with his staff. When he did, water had come out of it.
This time, God told Moses to tell the rock to give them some water. But instead, Moses hit the rock with his staff again, and water came out of it so the people could drink. Because Moses did that miracle the wrong way, God decided not to let him and Aaron bring the people into the promised land. So God sent Aaron to the top of a mountain, where he died.
The moral of the story
It’s not always a good idea to do what God told you to do, because sometimes he changes his mind.