"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."
Israel have grumbled once again. This time that there is no water for them and they worry that they will perish. It is good that they go to Moses and God to solve their problem, as we should take our problems to God in prayer today, but they were still in a state of unbelief and were complaining with the wrong attitude rather than humbly asking for help.
God's solution is to miraculously provide for them once again. He commands Moses to call forth the water from a rock. However, instead of verbally calling forth the water, Moses hits the rock and angers God. In fact, he hits the rock twice, which seems to indicate that he didn't believe once was enough for God either.
Because Moses did not do as God asked, he is not allowed to live to enter into the promised land. It might seem harsh that he suffer such a punishment for a moment of unbelief, but considering his example as an important leader and teacher, he is subject to stricter judgement. The same is true today for every preacher, pastor, and teacher - they must be careful to treat God's word (the bible) faithfully, and to uphold a high standard of conduct for themselves as an example to others.