(Numbers 20:12) Then the LORD spoke to Moses and Aaron, “Because you did not believe Me, to hallow Me in the eyes of the children of Israel, therefore you shall not bring this assembly into the land which I have given them.”Poor Moses! He went through an awful lot of trouble leading Israel. He put up with an awful lot of complaining and rebellion. Finally he lost his temper and lost his own opportunity to enter the promised land.
What are we supposed to learn from Moses' experience?
1) We need to believe God and act according to that belief.
God said that Moses failed because, "you did not believe me." Perhaps he didn't believe that speaking to the rock would be enough - he thought he needed to beat it a few times. Perhaps he didn't believe that this was enough of a rebuke to the people or enough vindication of himself and Aaron. At any rate, he did NOT do what God told him to do.
2) Our primary objective in every situation should be to exalt God as Holy.
It is very easy for us to think the situations we face are about us. They are not. We are all about glorifying God and enjoying Him forever. When Moses went after the rock he seems to have had a "I'll show you rebels a thing or two about who the prophet is..." attitude. In other words, he seemed more concerned about his own glory than God's.
So we feel bad about Moses, realizing that we are vulnerable to the same failures.
On the other hand we need to remember that actually arriving in Caanan was not the ultimate blessing. Moses still went to heaven. Many years later he communes with Jesus and Elijah on the mount of transfiguration. (Matthew 17:2-3) Moses was shut out of an earthly blessing, but he still had his heavenly reward.
Serving God is serious business. God will not be slighted.