The Torah describes the sin of Moshe Rabbeinu when he hit the rock, instead of speaking to it. Most commentators go with the text, and felt that Moshe did not sanctify the Name of G-d by not fulfilling His command. But there is also an opinion that says that Moshe’s real sin was that he gave in to anger. He should not have said, שמעו נא המורים, “Listen you rebellious people.” The emphasis from this story is to show how detrimental כעס, or anger, can be to an individual.
In the Iggeret Haramban, the Ramban’s famous letter to his son, he emphasizes this point. This was fatherly advice to a young son going off into the world. He told his son that the key to finding success in the world, is the ability to remove anger, from his personality. He even equated anger with Gehinnom, or hell. The reference to both anger and Gehinnom uses the word, רעה, or evil. Removing anger is like removing evil from a person.
If one conquers anger, all good things will be able to come. An individual will be able to achieve humility, which will lead to fear of G-d, as well as closeness to G-d.
Much has been written in the holy books that talk about how detrimental anger is to a person. The proof of this can be found with Moshe Rabbeinu. He paid the heavy price of not being able to enter the beloved Land of Israel.