Numbers 12

1 Apparently, Moses' first wife died and he married another woman. He did not take a wife who was a direct descendant of Israel. We are not told how the Ethiopian woman came to be involved in Israel.

God had strict commands against Israel intermarrying with foreigners. However, there were also laws that allowed foreigners to join Israel. It is likely that this was the circumstance here. We also know that Moses was close to God. Undoubtedly, they had discussed this matter beforehand. Aaron and Miriam were looking to gain some authority. They thought that they could elevate themselves by exposing some flaw in Moses. They went either to the other leaders or to the people of Israel with misleading charges.

The original language makes it clear that Miriam instigated this rebellion. Her name is listed first, and the verb "spoke" is in the feminine form.

2 They tried to bolster their argument by reminding the people that God had spoken to them in the past. Aaron was the high priest (and originally Moses' spokesman) and Miriam was a prophetess. What they failed to realize is that the current power struggle was their own idea, not a directive from God. They also failed to see that Moses' directives came directly from God. Aaron and Miriam wanted the people to listen to their leadership, not the leadership that came from God through Moses.
3 This statement was most likely inserted later by an editor, probably the same one who wrote about Moses' death. We know that Moses was reluctant when commissioned by God to lead Israel. As he learned to depend on God, he became humble. He did not try to assert his own authority; he simply did what God told him to do.
4 Before the rumor mill got out of hand, God intervenes in the situation Himself. He would not allow such divisions to come up now. Israel needed to be united in following God (and His chosen leader) if they were to enter the Promised Land successfully.
8 God spoke to prophets though dreams and visions. These visions were often filled with cryptic symbols that made the prophecy difficult to understand. However, God spoke plainly to Moses and used an audible voice. Moses did not see God's face, but from behind the cloud or veil, God spoke with Moses directly. No one else had this privilege. Furthermore, Moses had proven to faithfully say and do whatever God told him to do.
9 If Aaron and Miriam thought they could force God to recognize them as leaders, they were wrong. If they thought they could usurp Moses' God-given authority through the popular opinion of the people, they were wrong. Their selfish efforts met with a strong rebuke from God.
10 As punishment for leading this rebellion against God's chosen leader, God allowed Miriam to be instantly struck with a terrible skin disease. Aaron could have been punished as well for participating, but God does not do so. Perhaps God does not punish Aaron this way because of his position as the first high priest. The high priest was to remain clean, and a skin disease would have defiled him.
11 Aaron was more than remorseful that Miriam was being punished. He saw how foolish it was to question God's decisions. Miriam and Aaron had pride issues, while Moses humbly accepted his leadership role from God. Miriam and Aaron already had significant roles assigned to them, and they needed to learn to be content with them.

Aaron realized that he could not "force" God to do what he wished. God can not be bought, tricked, or bullied as mythological gods could be.

It is strange that Aaron cried out to Moses and not God. Moses neither made Miriam ill nor could he cleanse her. Perhaps Aaron was too ashamed or fearful of God to ask Him directly. Nonetheless, Aaron does confess their sin and asks for forgiveness.

12 A leper was placed outside the camp and not allowed to interact with the community. It was as if the leper was dead. Aaron compares a person infected with leprosy to a stillborn baby. There is sadness and grieving, but the baby must be buried. For the leper it is even worse since he remains alive although he is considered dead.
13 Moses also wants to see his older sister healed, so he prays to God -- the only one who can help her.
14 God indicated that He would heal her. This brief bought with leprosy was to humble Miriam. God did not think it pleasant, but He humbled her as a father would humble a rebellious daughter. A father spitting in his daughter's face would make her unclean for seven days. Miriam, likewise, would be isolated for seven days outside the camp. This was a stern reminder to her that God was in charge of making the political and spiritual appointments in Israel.
16 Once Miriam was accepted back into the camp, God led Israel closer to the Promised Land.