According to the interpretation of the Or HaChayim, the Torah portion of Acharei begins1 as follows: “G‑d spoke to Moshe [of] the death of Aharon’s two sons [Nadav and Avihu], who drew so close to G‑d that they died.”

The verse thereby indicates that Nadav and Avihu so adored G‑d, that though they realized that drawing too close to Him might result in their demise, this did not prevent them from striving for a union and ecstasy so powerful that it literally caused their souls to flee their bodies.

Earlier on,2 the Torah tells of Nadav and Avihu’s passing in greater detail: “Aharon’s sons … offered incense before G‑d … which G‑d had not instructed them.” The verse goes on to say that this offering led to their passing. Evidently, Nadav and Avihu’s drawing so close to G‑d that it caused their demise was related in some way to their offering incense. What was the relationship?

There is3 a fundamental difference between the spiritual service involved in bringing sacrificial offerings on the Outer Altar and the spiritual service involved in offering incense on the Inner Altar.

The main spiritual component of sacrificial offerings brought on the Outer Altar was the elevating of the physical to G‑d.4 Thus, physical animals were brought and their fat and blood were placed on the altar, whereupon a heavenly fire would descend and consume the offering5 — the animals would thus be elevated and incorporated within holiness. Consequently, the general intent of Outer Altar offerings was that man would interact with worldly things and elevate them to G‑d.

This was clearly not the case with regard to offering incense on the Inner Altar. There the main aspect of the service was the kohen’s entrance into the Holy — and on Yom Kippur into the Holy of Holies — so as to be able to unite and become one with G‑d through the ascent of the fire, incense and cloud of smoke.6

In terms of man’s individual spiritual service, the difference between the offerings brought on the Outer Altar and the incense offered on the Inner Altar is as follows:

The sacrificial offerings on the Outer Altar relate to the “external aspect of the heart,” so that the main emphasis is on the person’s fulfillment of G‑d’s will in thought, speech and action — these being the soul’s garments, not its essence.

The incense on the Inner Altar, however, relates to a more profound level of service, wherein an individual strives to cleave to G‑d by revealing his soul’s internal reality — that level which is always at one with Him. When this level is revealed, the person’s thought, speech and action will fulfill G‑d’s will as a matter of course.

This difference is also implied by the Hebrew root words for offerings and incense, korbanos and ketores. The word korban comes from the root karov ,7 which means “to draw close.” When an individual brings an offering, he draws close to G‑d. Still, it is entirely possible to draw close but nonetheless continue to exist as a distinct entity. Ketores, however, comes from the word katar ,8 which means “to bind,” i.e., the person becomes inextricably bound up and united with G‑d, becoming wholly one with Him.

The connection between Nadav and Avihu’s drawing so close to G‑d and the spiritual service of incense will be understood accordingly. Drawing so close to G‑d that one dies is similar to the offering of incense. In other words, Nadav and Avihu were conscious of and responsive to the intense internal level of union with G‑d that emanated from the essence of their souls. It was this feeling that brought them to offer ketores, thereby utterly attaching themselves to Him.

So intense was their feeling of unity that they offered incense without even having been commanded to do so; their union with G‑d was so intense that they knew instinctively what to do; a command was not necessary, for their unity with G‑d enabled them to be cognizant of His will.

Based on Likkutei Sichos , Vol. XXXII, pp. 98-101.