Come and see: When a man improves his deeds by [repenting of his bad ways and rectifying them] and brings an offering/korban, then everything is perfumed and [the higher “faces”/partzufim] come closer and then bind to each other in perfect union. Thus it is written, "If any man of you bring an offering" (Lev. 1:2), bring things to properly join them. [The Hebrew word for offering, korban, originates from the word kareb, meaning to draw close].

Come and see: "If any adam1 of you brings an offering" excludes any unmarried man, for his offering is not considered an offering and there is no blessing from him, either above or below. This is understood from the verse: "If any adam of you bring an offering." He is different because he is not a [complete] man [only half a man because his other half is missing] , he is not defined as “a man” [as referred to in the verse: “Male and female He created them and called their name Man/adam”… (Gen. 5:2)], and the Shechinah does not dwell on him because he is defective and is considered deformed [as a result of this lack]. A deformed man is distanced from everything, most of all from the altar and from raising up an offering on behalf of others. [The Temple service required that the sacrifice be without blemish and that the Priest who performed the sacrificial service be without any deformity – being unmarried was also considered a deformity.]

A man consisting of both male and female is worthy of bringing an offering...

Nadab and Abihu prove this, as it says in the verse: "And a fire went out from G‑d" (Lev. 10:2) Thus it is written, "If any adam of you bring an offering." A man consisting of both male and female is worthy of bringing an offering, but no other.

Rabbi Aba said, Although we interpreted the deaths of Nadab and Abihu in a different way, this explanation is certainly true as well. But [the main reason has to do with the incense because] incense is superior to any offering in the world, since for its sake the upper and lower beings are blessed. Yet they were not worthy of bringing this offering, which is higher than any other offering, as they were both unmarried. As such, they were not worthy of bringing an offering, let alone higher offerings [such as the incense] that all the worlds are blessed through them.

You may ask, why they were punished by death, as the verse says: "And a fire went out from G‑d, and devoured them." (Lev. 10:2) This is like the story of a man who came before the queen to announce that the king would come to her house and stay to rejoice with her. The man came before the king, and the king saw that the man was deformed. The king said, It is beneath my honor that through this crippled man I shall come to the queen. In the meantime, the queen prepared her house for the king. When she saw that the king was ready to come to her, yet that man caused the king to stay away from her, the queen gave orders to kill that man.

When Nadab and Abihu likewise came in holding incense, the Queen rejoiced and prepared herself to accept the King. When the King saw that these men were flawed and deformed, the King did not want to come to the Queen through them to stay with her. Thus, the King went away from her. When the Queen saw that it was because of them that the King was gone from her, immediately "a fire went out from G‑d, and devoured them."

...he who is unmarried is flawed and deformed in the eyes of the King...

The reason for all this is that he who is unmarried is flawed and deformed in the eyes of the King, and the holiness of the King is gone from him, for it does not dwell in a flawed place. Of this, it is written, "If any adam of you bring an offering." Let he who is considered adam bring it, but he who is not shall not bring an offering.

BeRahamim Lehayyim:
This Zohar is problematic for modern sensibilities, for it condemns as " flawed and deformed" any man who is not yet married. Such was the asserted sin of the sons of Aaron who brought an unsolicited offering of incense while single. Without reacting and simply writing this off as obsolete bigotry, instead we should try to wrestle with it and renew it.

Many single men yearn for a female life partner. They perhaps sense that when they are coupled, much of the energy they expend to find a woman may be now spent in building a home, a family, etc. Maybe this is the fear of the Zohar for those like the sons of Aaron who take on the sacred role of the priest bringing a special offering. That if they cannot give the complete focus to their mandate due to some unreleased sexual tension, this could fog up their required perfect contemplation.

While the unmarried priest should not bring the actual incense, an unmarried man seeking to nullify negativity might be well-recommended to say the verses of the incense portion found in traditional prayerbooks. It could be that this is just the thing to center him, and thus open up his path to meeting his true soul-mate.

[Bracketed annotations from Metok Midevash and Sulam commentaries]