The Chasam Sofer explains why people so easily stumble with forbidden speech. When a person speaks lashon hara, he thinks, 'I am not really doing anything wrong. It is only words, not a physical action that can have an effect.' Thinking this way is a grave mistake. A word spoken has immense power and if it is a negative word, can be extremely damaging.
Had Moshe Rabbeinu spoken to the rock, Klal Yisrael would have witnessed the enormous power of speech. They would see how just a few spoken words can quench the thirst of a crowd of millions and their cattle. Alas, when Moshe hit the rock, the opportunity to demonstrate this crucial lesson was lost, eventually giving way for the baseless hatred caused by improper speech which caused the second Beis Hamikdash to be destroyed.
(חתם סופר - תורת משה)
