The second proffered motive stuck with me; in a comment I discussed the "random" part of God's behavior, but here I wanted to look at the vindictiveness.
We need: “Crime Scene Investigation: Shemini”
Our primary suspect is Hashem. We have multiple eyewitness accounts that place the suspect at the scene of the crime. Our main task therefore is to establish a motive. Since the suspect has been historically unresponsive to direct questioning since the time of the Prophets, not to mention the fact that I’m pushing my luck with all the God jokes so far, I am content to use the evidence we have at hand to derive some conclusions.
Possible motives would include:
- God requires perfection
- God is random and vindictive
- Nadav and Abihu purposely engineered their own death
- Nadav and Abihu did something extremely horrible, the consequence of which was death
The Old Testament Yaweh does have a vengeful - that is to say vindictive - streak. "I do this because of what he has done unto me" is a common theme. It may not be random; it may even be logical. Many temporal rulers and scholars of power have strongly believed that to maintain a rule, and keep your subjects proud of their ruler, a king must act against any insult offered him. Not out of emotional needs for vengeance, but in the same way you would put down any crime. Still, it is hard to label such behavior as anything but vindictive. For that matter, many people suggest that punishing any crime is more about retribution than rehabilitation.
God in the Old Testament is, right or wrong, a bloodthirsty deity; we all know that. Look at the swath of blood God leaves behind Israel in leading them from Egypt to the Promised Land. Then, suddenly, we reach the New Testament and the bloodshed stops. (Well, slows down considerably. And is done with much more apology.) I always figured this was because after generations of trying to get his followers to kill their own sons, but being stopped at the last minute (usually), God finally succeeds at killing his own son. As so often happens, death of a loved one is a growth experience, helping Adonai mature, develop greater empathy, and realize what a dick he was being to many people. After that the demands to sacrifice, commit genocide, and be vengeful and vindictive stop coming from divine sources. Plenty of human sources still encourage such action in God's name, but it's not fair to blame God for his followers.