In Bamidbar 12, we have the story of Miriam becoming Leprous due to her criticism of Moshe’s apparent unwillingness to take a native Israelite as a wife. Moshe married a Kushite, and to Miriam, this was kind of a slap in the face to Israelite women. I don’t know what exactly it was that Miriam was upset about, but, like some siblings do, they must have called a family meeting without inviting the subject of discussion and hashed over the thoughts among themselves. I have no doubt that my mother called a few of those herself on my behalf without asking for my personal participation.
It could be that Moshe’s wife, coming from a different culture and race, created a political trap for Moshe. Perhaps Miriam felt that a leader-king of Israel should have as a mate a woman who is thoroughly Israelite-ish herself, if for no other reason than to show the people, by example, that Moshe, once an Egyptian heir, was truly one of those he sought to govern. Miriam may have seen this marriage to this non-Israelite, as an underlying cause for the persistent rebellion against Moshe’s authority; a rebellion which they did not carry out against Aharon, who seemed to curry more favor with the people. In politics, having a leader who doesn’t share your socio-economic or cultural background sometimes causes the governed to become suspicious of the ruler’s motives. This was clearly evident in Russia, where the people became emotionally predisposed to revolt based upon the Czar’s marriage to a catholic German princess. Moshe just seemed too strange already to the simple Israelites in too many ways, and by taking a bride from another race just made matters worse. This was likely what Miriam was complaining about. It is also likely that she was genuinely concerned for the safety of her little brother, and there was no guile or ulterior motive to her complaint. HaShem, however, did not think it was an issue and struck Miriam with leprosy as punishment for her speaking out. Verse 12:2 bears this out when Miriam says what she believes the people are thinking. She is right.
So, what turned this very accurate and insightful political observation into Loshen Hara and worthy of severe punishment? The fact that Moshe and his wife were not invited to the meeting or that the concerns, legitimate as they might have been, were not shared directly with Moshe. Even speaking from caring and concern without the subject being present is a form of Loshen Hara. The next question is why Leprosy as opposed to some infection of the teeth, gum, or larynx which would seem fitting since that’s where the words came from?
There is a story about the Chofetz Chaim, known for his crusade against Loshen Hara, that as he was aging he began to lose his hearing. A student once asked him. “Rabbi. Aren’t you worried about going deaf?” The Chofetz Chaim thought for a moment and replied, “Well. At least I can be pretty sure at that point that no one will approach me to shout Loshen Hara into my ears.” Loshen Hara, as a phenomena, is a social disorder; there has to be someone to tell it to. Leprosy’s punishment is not that one becomes ill, but that one resides alone while in quarantine and is forbidden from maintaining social contacts. As the song says, “One is the loneliest number.” Thus, a disease requiring quarantine is the best spiritual medicine for gossip.
So, when Aharon pleads with Moshe not to cut Miriam off from family and friends he says “Don’t allow her become like a dead person” i.e. bereft of social contacts, shunned, and eventually forgotten. For Miriam, who was from the beginning of his life a caretaker for Moshe, to be cut off from him and his work would be devastating. Therefore, she was struck with leprosy, and it is comparable to death insofar as it signals an end to her reason for living. Such is the maternal love of a sister for her baby brother that she would risk the wrath of HaShem on his behalf.
Moshe should have considered himself very lucky.