According to Seder Olam, the Mishkan (Tabernacle) was erected on the 23rd of Adar during Israel’s second year at Sinai. The next seven days, Moses taught the offerings, as well as daily service performed by the kohanim and Aaron, who would be Kohen Gadol (High Priest). Moses also demonstrated how to dismantle and reassemble the Mishkan every day. Parashat Shemini (Lev. 9:1–11:47) opens on the eighth and final day of this inauguration. The number eight represents completion but more importantly, it represents elevation above the natural realm--an apt description for the awe-inspiring arrival of the Shekinah. Before this dramatic experience can occur, Moses reminded the kohanim and the people that it was critical to follow HaShem's direction.
"Moses said: “This is what HaShem has commanded that you do, that the Presence of HaShem may appear to you.”
With those words in mind, Aaron and his sons carefully completed a series of korbanot (offerings). Moses then joined Aaron to enter the Mishkan. When they emerged and blessed the people, a vortex of fire descended onto the Holy of Holies in the Mishkan, flowing outward to consume the offerings.
No wonder the people fell on their faces, praising the Creator.
This joyful and momentous day came to a standstill when the sons of Aaron, Nadav and Avihu, suddenly approached the Mishkan with "strange fire" and died instantly. There are over ten reasons suggested for their demise; everything from being intoxicated, refusing to marry, or their pride. But the Sages defend Nadav and Avihu as possessing a level of holiness that was akin to their own father and their uncle Moses. Rather than character flaws, they may have gotten so carried away that they forgot that, in some instances, boundaries are a necessity for keeping HaShem's commandments. The last time Israel came physically close to the presence of Creator was just prior to the giving of Torah, when the people are repeatedly warned not to stray too near Mount Sinai:
"Ha Shem said to Moses, “Go down, warn the people not to break through to HaShem to gaze, lest many of them perish. The priests also, who come near HaShem must stay pure, lest HaShem break out against them.” - Exodus 19:21-22
Bar Kappara, a rabbi of the late 2nd and early 3rd century focuses on these kinds of missteps that could have led to the death of Aaron's sons. He taught , in the name of Rabbi Jeremiah ben Eleazar, that Nadav and Abihu died because of four things: (1) being too near the holy place, (2) making an unauthorized offering which was (3) fire brought from a kitchen, and (4) not having taken counsel from each other. In effect, the brothers followed their own initiative.
Even so, HaShem said that, “I will be sanctified through those near to Me, and before all the people I will be glorified.”
As Rashi taught, a stricter level of conduct is required of those closest to HaShem. The fate of Nadav and Avihu reveals how the kohanim, in fact all of Israel, must follow Torah in a prescribed manner, whether constructing the Mishkan, compounding the Qetoret (incense), bringing the korbanot or even the way to live one's life. Even an architect knows that if you ignore certain details, the building will collapse. The importance of following the laws of Torah is underscored by God telling Aaron:
“This is a law for all time throughout the ages, for you must distinguish between the sacred and the profane, and between the impure and the pure; and you must teach Israel all the laws which HaShem has imparted to them through Moses.”
The death of Nadav and Avihu serves as a tragic example that the "heart is deceitful above all things." These righteous young men were led astray by their religious fervor, ignoring the clear dictates of HaShem. They attempted to innovate during the Divine service. Western society and literature constantly tells us to "follow your heart" as if the heart is the ultimate depository of truth. Judaism teaches the opposite: follow the dictates of God, the Creator of Truth--only then can your heart truly lead you. To this, we can offer this valuable principle from the Sages: The heart follows action. To be good, you have to know what is good and then you have to DO what is good.
God loves innovation but when confronted with an awesome display of power we barely comprehend, God’s instruction is even more critical. That’s why the concept of the Mikvah and the laws of Kashrut are also taught in this portion of the Torah. Whether it’s eating kosher, properly slaughtering an animal or priestly service in the Sanctuary, ignoring the Creator’s directions, diminishes holiness and can even lead to destruction. Purity in mind and body sustains life and elevates the soul above the natural realm.