Aaron’s two elder sons, Nadav and Avihu were participating in the ceremony of the dedication of the Tabernacle. It was the inauguration of the ceremonial role of the priests and the final reconciliation of everyone after the Golden Calf rebellion. It’s the finale of the ceremonials.
The sacrificial rituals were performed and fire came from the sky, struck like lightening and burnt up around the altar. All the onlookers were shocked, amazed. It was a show of Divine power as well as approval.
Immediately afterwards Aarons two sons decided to go in, on their own initiative, and perform their own ceremony. As they brought their incense towards the altar, fire shot out again and this time burnt them to a cinder. What were they thinking? They had seen the Divine Fire just before. How were they not frightened of taking risks? What was their motive? The Torah say explicitly that they did something they were not commanded to do.
There are lots of different explanations the rabbis give; they were drunk (laws follow forbidding priests to drink and serve), they were arrogant heirs and wanted to take over right away (the Midrash says they walked behind Aaron and Moshe saying, “when will we take over.” Perhaps they thought they could do things better ceremonially. Maybe they were just trying to be more religious, stricter. Instead they turned the rejoicing into a disaster.
If they thought they could do things differently or better than their elders, surely, they could have discussed it. But instead of trying to work with them they decided to override them and take the law into their own hands.
There is a fine balance between innovation and rebellion. Every new generation wants to take over and try to do things better. But this may mean undermining the previous generation. One runs the risk of destroying before one has succeeded in putting a better solution in place. The ideal is to find a balance between respecting the past and our seniors and moving towards change. This is why the Torah tells us to respect the elders but at the same time requires us to deal with new situations through the halachic system. The leaders of each generation make their own decisions. But ideally based on what has come before.