Many of the great rabbinic exegetes to the torah hold that the reason that Moses was not permitted to enter into the Promised Land happened in this Sedra. The people were thirsty and wanted water. For reasons that seem exaggerated to us, they feared that they would die of thirst in the desert. (How they could thus fear does not make any sense. All the time that they traveled in the desert, they had sufficient food to eat. They always had proper shelter. They did not want for a thing.)
They turned to Moses, and as usual complained to him. They demanded that he find them water to drink. Moses turned to God Who told him that water would come if Moses spoke to the rock.
The people continued to complain, and Moses lost patience, so instead of speaking to the rock, he hit the rock and water began to flow. The people were satisfied for the moment, but Moses had sinned by his action. He hit the unfeeling rock instead of speaking to it. By his action, Moses sinned against God Who said "Because you did not have faith to sanctify Me before the Children of Israel, you will not lead the congregation to the land that I promised to them.
Why was the punishment for that sin so severe? The people did not know that Moses did wrong when he hit the rock instead of speaking to it. And in any case, the rock was not alive that it could hear the words of Moses. The rock was only a rock in a dry place. Hitting the rock made the dry place wet, and that was enough for the people.
However, how we deal with the world influences the way that we deal with people. People who hit rocks often hit animals and even people. Child abuse and spousal abuse do not come from a vacuum. Those who act out violence against those they love had to learn to be violent in all aspects of their lives.
The rock could not hurt, but at some time violence against God's creation could hurt. When was that point reached? Moses would know only after he crossed that line. God, therefore, demanded that Moses, role model that he was, act in a peaceful way in all that he did. He was never to sanction violence in everyday actions.
He needed to teach people the power of talk. He needed to show by example that violence is not the way to bring peace to the world. To a people that often were blind to the presence of God, but not to the presence of Moses; Moses taught otherwise. He gave the people reason to act violently in their lives, and so Moses was not allowed to enter the Promised Land.