In the beginning of the parsha, Rashi asks why the parsha of the spies is juxtaposed with that of Miriam speaking against Moshe. He answers that the spies saw what had happened with Miriam and didn’t learn the lessons of speaking loshon hora.
This answer may seem a little problematic. Why would they learn mussar from Miriam, who was speaking against her brother? After all, they were speaking against the insentient, inanimate land.
The Rambam points out in Hilchos Melachim (2:6) that the greater a person is, the greater must be his exercise of humility (in its real sense), based on the possuk, ולא ירום לבבו. The greatest of all men was Moshe, about whom the possuk says, ‘והאיש משה עניו מאד מכל אדם אשר על פני האדמה’ – ‘Moshe was more humble than any person on the face of the earth’. The words in bold seem a little bit hyperbolic. But according to our understanding, the meaning could be that his level of humility was such that he made himself impervious to personal feelings of sensitivity, like the ground itself, which is insentient.
In this case, the spies should have taken heed of the fact that Miriam had been punished for speaking ill of someone who was totally removed from feelings on the subject.(Indeed, he completely forgave her and davened on her behalf.) This being the case, we are able to grasp Rashi’s comment about the juxtaposition of the two events.
It goes without saying (although I’m saying it), that we have a real lesson about sensitivity in speech to be learned from here. In both cases, the error in speech was much more subtle than a straightforward, nasty piece of loshon hora. Yet we have Tisha B’Av and all the tragedies of Jewish history that have ensued as a result. Conversely, if we use our lips for their correct purpose, think what we could achieve.
-From the sefer ‘Siach Sarfei Kodesh’