The punishment that God brought upon Miriam was meant as a lesson of the severity with which God punishes slander. For Miriam spoke no evil of Moses in the presence of any one except her brother Aaron. She had moreover no evil motive, but a kindly intention, wishing only to induce Moses to resume his conjugal life. She did not even dare to rebuke Moses to his face, and still, even in spite of her great piety, Miriam was not spared this heavy punishment.
Her experience, nevertheless, did not awe the wicked man who, shortly after this incident, made an evil report of the promised land, and by their wicked tongues stirred up the whole people in rebellion against God, so that they desired rather to return to Egypt than to enter Palestine. The punishment that God inflicted upon the spies as well as upon the people they had seduced was well deserved, for had they not been warned of slander by Miriam's example, there might still have been some excuse. In that case they might have been ignorant of the gravity of the sin of slander, but now they had no excuse to offer.