Why was God so upset with Moses for striking the rock the second time in the desert? In Exodus, God commands Moses to strike a rock, and promises to make water flow in the desert for the people.


  Behold, I will stand before you there on the rock at Horeb, and you
  shall strike the rock, and water shall come out of it, and the people
  will drink.” And Moses did so, in the sight of the elders of Israel.
  (Exodus 17:6 ESV)


Later on, God tells Moses to speak to a rock, promising to make water flow in the desert again.  However, Moses strikes the rock again instead of speaking to it.  Because of just this one thing, God tells Moses that he will no longer be permitted bring the people into the Promised Land.  


  “Take the staff, and assemble the congregation, you and Aaron your
  brother, and tell the rock before their eyes to yield its water.
  So you shall bring water out of the rock for them and give drink to
  the congregation and their cattle.” 9 And Moses took the staff from
  before the Lord, as he commanded him. 10 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?” 11 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. 12 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.” (Numbers 20:8-12 ESV, emphasis added)


Why was the punishment so harsh for what seems like a small infraction?  Was there something greater or more symbolic going on here?
Like the forefathers of those who eventually ended up in the Promised Land, Moses's problem was that he failed to trust in God. In chapter 12 of Numbers, Aaron and Miriam oppose Moses as  God's messenger and their leader. As a result, they also are refused entry to the land (by death, like Moses). 

Moses' problem wasn't that he misinterpreted God or thought that since he'd hit the rock before that it was okay to do it again. Rather, Moses was utterly rejecting God and trying to take control. 


Moses was violent. He struck the rock twice when God just said to speak to it. 
Moses was usurping God's place. He said to the people, "hear now, you rebels: shall we bring water for you out of this rock?" The emphasis is technically mine, but it was already there. Moses didn't say "God will bring water out of this rock for you." He (with Aaron, evidently) took God's place and assured them that he would do it for them.


Verse 12 is pretty revealing as to the nature of Moses's crime: 


  "Because you did not believe in me," (emphasis mine)


Moses totally failed to trust God for the life-supplying water. He tried to take matters into his own hands. He was supposed the be the leader, but also the servant of God. He tried to usurp God's place.

Additionally, I think there might be some symbolism to the rock. Back in Exodus 17, God tells Moses


  "Behold, I will stand before you there on the rock at Horeb, and you
  shall strike the rock, and water shall come out of it, and the people
  will drink" Ex. 17:6


To quote my study bible notes on this, "An astonishing statement. In this trial God takes the place of the accused, standing in the dock."

1 Corinthians 10:4 explains that "the Rock was Christ." In striking the Rock, Moses was striking God for the people. Christ was punished for the nourishment of his people.

Back to Numbers, it seems that maybe the situation is similar here. God has provided a rock (Christ) that will bring forth water (salvation) for his people.  This is somewhat speculative, but it seems that this time, Moses is in the position of the people. He's supposed to ask God for salvation, to request the water from the rock. But instead, he takes up his previous position as judge, and strikes the rock (Christ). Before, he was commanded to. This time, he willingly strikes his Savior.

It's interesting to note, in support of that theory, that the Hebrew word used for "strike"  is the same in both cases (link), and the words for rock are quite similar (Numbers word &amp; Exodus. word)

Ultimately of course, it's because Moses did not believe that God could bring the water out of the rock, and hit it himself. (perhaps he was trying to knock loose rocks to open up a stream, or he thought that his staff held some special Mosaic power - either way, he thought he was the key to the equation)



I used my study bible a good deal on this one, the ESV Reformation Study Bible by Ligonier