Lord Sack's dvar torah may be found at: http://www.israelnationalnews.com/Articles/Article.aspx/10098
I highly recommend it. He also delivers it as a video on the same page.
I was honored today to attend the bar mitzvah of one Jonathan, son of friends Marsha and Doug, a young man I've known literally from the womb. He did a fine job leading elements of the services and reading his Torah portion and his Haftarah. His parsha was Shmini, which means "eighth".
Following extensive instruction on the construction of the Mishkan, and the account of the actual construction, in Exodus, Leviticus opens with instructions on how to get the place up and running. There are seven days of preparation and ritual, the same time it took to create the world, rest included, the same length of time a wedding was celebrated in the time of the patriarchs. On the eighth day, as a boy is brought into the Abrahamic covenant, the Kohanim officiate for the first time as fully installed, fully consecrated priests.
Moses and Aaron, at the end of chapter 9, make a sacrifice, go into the tent, come out, bless the people, and Divine fire consumes the offering, to the delight of the crowd. The very next thing that happens is that Aaron's sons, Nadav and Avihu, ignite strange fire, and Divine fire consumes them.
The Chief Rabbi of England, Lord Sacks, another Jonathan, delivered a learned and fascinating Dvar Torah on this week's Parsha, in which he discusses the incident of Aharon's sons offering strange fire. He compares the spontaneity of this incident with that of Moshe in shattering the first Luchot haBrit, the tablets containing the Ten Commandments. He points out that the requirements of Kohanim, priests, and of Prophets, Nevi'im, are different. Prophets deliver a different message each time the Divine Spirit flows through them. Conversely, Priests are given explicit instructions, and are expected to follow them implicitly. This, he says, is why Orthodox Judaism has prescribed prayer: it is the offering we make in place of the prescribed sacrifices, which are impossible in the absence of a functioning Mikdash, Temple, on Har haBayit in Jerusalem. While what he says is true, it seems to me that he ignored the most important difference between the incidents: motivation, in Hebrew Kavanah.
When Nadav and Avihu sinned, they offered strange, Zar in Hebrew, fire. The fire is called Zar, strange, and this is clarified by the phrase "asher lo tzivah otam", "which He had not commanded them". Strange, not in the sense of odd, which would be Meshuneh, but in the sense of foreign. They acted, as newly installed priests inside the Mishkan, the portable Temple, out of personal, one might say selfish, motives. They misused holy objects and holy materials in a holy place. Was it just to enjoy their role as priests, or did they offer fire to foreign G-ds? I don't know. Their INTENTION was not to fulfill their mandated function. The fire they placed in their pans was not commanded.
Moshe descended the slopes of Sinai, and saw the people, very Nadav and Avihu like, cavorting and disporting and partying up a storm about an idol that, I suspect, was not an Egyptian deity, but the preJewish Semitic Bull Hadad (http://doctor.claudemariottini.com/2010/09/hadad-moabite-god.html). Moshe saw his people reverting to preAbrahamic practices, and out of fury over their sin, expressing his own intense dedication to G-d, he smashed the tablets before them. This is why Rashi praises the action in his last commentary on the Torah.
It is the intention of the act, dedication or disobedience, that determines its acceptability, not its spontaneity.