Miriam’s Bad Judgement
There is a Tosfot in Masechet Yevamot that explained the background to the incident where Miriam spoke Lashon Hara against Moshe.
Tosfot is commenting on the Gemara’s claim that Moshe Rabbeinu decided on his own after coming down from Mount Sinai, that he would no longer resume marital life with his wife, Tzipora. Hashem agreed with Moshe’s idea that he needed to be in a state of purity at all times.
Tosfot further claims that Miriam was not aware that Moshe had taken this step, until she spoke to her sister in-law. This took place when there was excitement in the camp that Eldad and Meidad were given the gift of prophecy.
Miriam then said to Tzipora that their wives must be so proud that their husbands achieved this achievement. Her response was that the wives won’t be so happy when they will no longer be intimate with their husbands.
Miriam was shocked and ran to tell Aharon. She thought it was wrong since she and Aharon were also prophets and they maintained normal marital life.
She was punished for this as she should have realized that Moshe’s level of prophecy was much greater than hers. She should not have spoken Lashon Hara against her brother.
Tosfot with the help of the Sifrei gave us the background to get a clearer understanding of the story.