Why Moses wasn't allowed to enter the Promised Land

“But the Lord said to Moses and Aaron, ‘Because you did not trust in Me enough to honour Me as holy in the sight of the Israelites, you will not bring this community into the land I give them.’” Numbers 20:12
In Numbers 20 we have the second accound of Moses bringing forth water from the rock for the children of Israel. This had happened once before, at Rephidim, very early in their travels (Ex. 17:1-6). There, Moses was instructed to strike the rock. He did so, and water gushed forth for the people to drink. Here, the people are again complaining, and Moses again strikes the rock, saying, “Listen, you rebels, must we bring you water out of this rock?” (Num. 20:10).
It might seem like a hefty punishment: Moses had been faithfully leading the people for forty years, and this one incident rendered him ineligible to enter the promised land. But Moses had misrepresented God to the people on two accounts. First of all, Moses gave them impression to the Israelites that God was angry with them, but He was not. Secondly, God had told him to speak to the rock, not strike it. It might seem like splitting hairs, but God was trying to teach the Israelites something, using the rock as a pattern. Paul tells us, “They all ate the same spiritual food and drank the same spiritual drink; they drank from the spiritual rock that accompanied them, and that rock was Christ” (1 Cor. 10:3-4). Jesus is called a rock or stone in prophecy (Ps. 118:22, quoted in Acts 4:11). If Moses had obeyed God, the water from the rock would have provided a beautiful picture: the first time, Christ was smitten, and living water poured out (John 7:37-39). The second time He comes, He will not be struck again, but simply spoken to, and will provide salvation for Israel (Hos. 5:15, Zech. 12:10).