Then came the people of Israel, the whole congregation, into the desert of Zin in the first month; and the people abode in Kadesh; and Miriam died there, and was buried there.
And there was no water for the congregation; and they gathered themselves together against Moses and against Aaron. And the people quarrelled with Moses, and spoke, saying, 'Would G-d that we had died when our brothers died before the L-rd! And why have you brought up the congregation of the L-rd into this wilderness, that we and our cattle should die there? And why have you made us come out of Egypt, to bring us in to this evil place? This is no place of seed, or of figs, or of vines, or of pomegranates; nor is there any water to drink'
And Moses and Aaron went from the presence of the assembly to the door of the Tent of Meeting, and they fell upon their faces; and the glory of the L-rd appeared to them. And the L-rd spoke to Moses, saying, 'Take the rod, and gather the assembly together, you, and Aaron your brother, and speak to the rock before their eyes; and it shall give forth his water, and you shall bring forth to them water out of the rock; so you shall give the congregation and their beasts drink.'
And Moses took the rod from before the L-rd, as he commanded him. And Moses and Aaron gathered the congregation together before the rock, and he said to them, 'Hear now, you rebels; must we fetch you water out of this rock?'
And Moses lifted up his hand, and with his rod he struck the rock twice; and the water came out abundantly, and the congregation drank, and their beasts also. And the L-rd spoke to Moses and Aaron, 'Because you did not believe me to sanctify me in the eyes of the people of Israel, therefore you shall not bring this congregation into the land which I have given them.' --Numbers 20:1-12
But what was the mistake? Striking the rock instead of speaking to it? Thirty nine years earlier, Moses was commanded to strike the rock to bring forth water. Why would this be such a tremendous error, one that brings such a sentence? Some of this has to do with spiritual maturity - going from physical to spiritual. In the beginning, it might have been that Hashem was stepping Moses through obedience, through physical action to build his faith. However, after thirty nine years, he was not to be a man of action but a man of words. His spiritual greatness would have allowed Hashem to work through him merely by speaking - and speaking words of life, not anger.
However, while this is a standard thought among the Sages, I would like to add another dimension. I also believe that with spiritual greatness, there is the responsibility to show patience and love to a people which one serves. The outburst of "hear now, you rebels; must we fetch you water out of this rock" does not show patient leadership, but rather something else. However, before we get down on Moses, perhaps we need to step back further in the passage to understand how Moses got to that place of losing his patience.
In the preceding passage, it speaks of how the people came to Moses and Aaron and they were complaining. They had just lost Miriam, the prophetess to the people, sister to Moses and Aaron. Miriam possessed such a depth of holiness and desire to serve Hashem that her presence among the nation of Israel merited the physical manifestation of the ever present mayim chayim (living waters). Moses was also an agent in bringing forth water and spiritual revelation. Following the death of Miriam, the Sages say that the waters dried up. Hashem realized the people were suffering spiritually and physically from losing the spiritual giant that was Miriam. He saw they needed not only their thirst abated, but also to feel the Divine presence in their midst in a miraculous way yet again. Hashem's command to speak to the rock might have been a task that Moses, in his state of loss, found difficult to perform. However, instead of speaking to the rock, we learn that Moses struck it twice.
Perhaps in his mourning, the frustration and impatience he felt toward the people and the loss of the well so overwhelmed him that he temporarily caused him to lose control. In his brief moment of action, it was not only an offense to Hashem by not sanctifying Him through speech, but also an affront to the memory of Miriam. Her life embodied the ability to produce water and to do so in a manner of patience and obedience to Hashem: the result of this was nourishing water and prophecy, a life of honor and benefit for all.
But let's step back from the sin of Moses. It is important to remember that the people, in their impatience and mourning helped to bring Moses to a place where he was challenged. In a sense, the contagious impatience and the reigning spirit of disgruntledness of the people overtook the camp and so much so that it spread to the leadership. This is where impatience affects not only one person, but a multitude. It would be hard to imagine that Moses intended this transgression; however, the spirit of the people literally infected the camp and for one reason or another, Moses was not immune to it and allowed it to overtake him.
This crowd mentality can speak volumes to us individually. What can be a difficult moment for you might become a difficult moment for many if your emotions of anger and impatience manifest in your behaviors. Even the greatest among us can be tried by being in the presence of those who lack the ability to compose themselves in a patient and long-suffering manner.
The next time you feel yourself losing patience over a situation, remember this warning: impatience is contagious.