Then Moses and Aaron gathered the assembly together before the rock, and he said to them, "Hear now, you rebels: shall we bring water for you out of this rock?" And Moses lifted up his hand and struck the rock with his staff twice, and water came out abundantly, and the congregation drank, and their livestock. And the LORD said to Moses and Aaron, "Because you did not believe in me, to uphold me as holy in the eyes of the people of Israel, therefore you shall not bring this assembly into the land that I have given them." (Num. 20:10-12)Just exactly what did Moses do wrong? The text indicates a couple of things-
1) Moses spoke harshly to the people. When the Lord told Moses to speak in 20:8, He told him to speak to the rock, not the people. Not only did Moses speak to the people, but he spoke harshly to them. I can certainly understand why he lost his cool with them. As the psalmist wrote later:
They angered him at the waters of Meribah,
and it went ill with Moses on their account,
for they made his spirit bitter,
and he spoke rashly with his lips. (Ps. 106:32-33)
2) Moses struck the rock instead of just speaking to it. Nowhere in God's instructions did He tell Moses to use his staff (unlike His instructions in Ex. 17:6). Moses was to tell the rock to yield its water, rather than to strike it, which would be an even greater display of God's power. But Moses acted in a way that obscured the power of God.
3) Moses acted with a "high hand." In 20:11 the text says "Moses lifted up his hand." This is the same language that is used in 15:30 to describe those who sin with a "high hand." The text may be implying that Moses acted with a presumptuous spirit in striking the rock twice rather than doing what God said.
As a result of this, Moses could not enter the Promised Land after leading the people so long and through so much tribulation. God takes His holiness seriously, and since Moses did not uphold God as holy before the people (20:12), he paid a heavy price.