How to become a priest. Keep your incenses straight!
Moses gives Aaron and his sons a ritual bath, then dresses them in the priestly robes. They sacrifice a bunch of animals in the painstakingly detailed ways described in the preceding seven chapters, which you can see here in Lego. Moses then tells them to stay in the bloody, oily, smelly, temple for seven days to finish their investiture.
On the eighth day, Moses returns and tells them to sacrifice even more animals. This time, they include a calf, the only time this sacrifice is mentioned, to atone for the golden calf episode in Exodus. God sends down some fire to consume the burnt offerings, and the people fall on their faces. In prayer, or biblical slapstick, it isn't clear.
Aaron's two sons fill a censer with strange fire (v. 1). So god burns them to death. What the strange fire is not clear. Jerry, for once being helpful, has 4 theories: 1) They were the wrong coals 2) it was the wrong time of day 3) only the high priest was permitted to put the coals in the censer 4) they were intoxicated. There's a reason why all the good drugs and 3 major religions come from the same place, yo. The point, however is: make damned sure you have the right incense people, because god gets mighty pissy if you don't.
Moses, the paragon of sympathy, tells his brother it was for the glory of god, and not to mourn, lest god kill him, too. Boy, I bet those Israelites are glad they chose that one all-powerful god over the loose coalition of less-powerful Egyptian gods now! He orders some of their cousins to carry the bodies away. He also forbids Aaron from leaving the tabernacle on pain of death.
The next rule for priests is no drinking. Penalty: death. He says this is a rule forever. Jerry says it's so nothing interferes with their ministry. Hmm... loads of religions allow their priests to drink. And the leaders of every church leave sometimes. I wonder how they justify that.
Moses next tells them to keep themselves holy and clean, so they can teach the others. Finally he tells them to make a sacrifice and eat the meat. But they don't eat the meat, and Moses gets angry. Aaron points out that his sons had eaten their offerings that day, and died, so would god be pleased with him, too? This shuts Moses up.
I cannot emphasise this enough, people: make sure it's the right incense!