As it becomes operational, the Mishkan (Tabernacle) engenders new responsibilities: Aharon is commanded to abstain from intoxicating beverages as he is called upon to function as kohen. At first glance, this prohibition appears to be a practical precaution against the debilitating effects of alcohol and the diminished capacity often associated with drinking. There are, however, rabbinic traditions that read this commandment as ominous foreshadowing, linking it with the sudden, tragic deaths of Aharon's two sons on that very same day. According to this view, Nadav and Avihu were intoxicated when they approached the Mishkan on the eighth day of its consecration, and the results of their impaired judgment were fatal.
Despite this alternative reading, we need look no further than the Torah text itself to understand the new commandment given to the kohanim. In somewhat unusual form, the Torah offers an explanation of the inner workings of this prohibition: "To separate between the holy and the mundane and between the impure and the pure." When properly understood, this commandment speaks to the very core of the Mishkan, and for that matter, the entire book of Vayikra.
While Vayikra begins with the completed Mishkan and the laws that will frame and enable the service of the kohanim, the focus and scope of Vayikra's legal purview quickly expand to encompass each and every Jew, in all areas of life, to include such matters as permitted and forbidden foods, as well as permitted and forbidden sexual partners. In each of these cases, the legal precept is described as creating a "separation."
The commandments transmitted in the book of Vayikra are not the first mention of the concept of "separation." In the Torah's opening verses, the creation of the world is described as a process of separation - between darkness and light, between water and water. By definition, separation indicates distinction, but is not necessarily indicative of a value judgment. The separations through which our physical reality was created may be understood in terms of utility, and we may easily imagine that the Torah could have described the Divine act of Creation without employing the terminology of separation.
In the description of creation, the only use of the concept of holiness was in the context of Shabbat, the day that commemorates the acts of separation through which God created the universe. On the other hand, in the process of creating the Mishkan, the concept of holiness is the dominant theme, but up to this point, no explicit mention has been made of the concept of separation. Only now, as the unique commandments regarding Aharon's comportment in the Mishkan are recorded, the cross-pollination of these ideas comes to fruition. The Mishkan, a construct dedicated to holiness, is a microcosm of a new world, a world in which mankind can access holiness. Therefore, when man is called upon to build the Mishkan, inherent in the process is a series of acts of separation that lead to a state of holiness.
One of the most axiomatic concepts taught by our sages is that holiness means separateness. To be holy is to acknowledge, to internalize and to act upon concepts of separation and separateness, gradations and seemingly slight differences that permeate and define time, space and matter. In Parashat Shmini, the vehicle through which the Torah conveys these concepts is designed to point our attention toward the need for clarity regarding the delicate separations that lead to holiness: Kohanim must not drink wine before serving in the Mishkan. In the mystical tradition, the Tree of Knowledge of Good and Evil - the tree at the center of the Garden of Eden whose fruit causes confusion and leads to death - was a grapevine. When fermented, the fruit of this tree intoxicates and confuses us, and leads us to overstep boundaries, to overlook the subtle separations that create holiness. In this respect, the tragic story of the deaths of Aharon's sons, and the prohibition against drinking by the kohen - both of which emphasize "separation" - serve as an introduction to all of the book of Vayikra.
The creation of holiness causes unavoidable collateral damage, for only when we become aware of the holy can we become sensitive to what remains outside the parameters of holiness: The creation of holiness gives rise, unavoidably, to the profane. Whereas the amorphous condition of "unholiness" had been the status quo ante, only now, in sharp distinction to the radiant, uplifted state of holiness does the unholy suddenly seem dark and dreary. Before there is holiness, there cannot, by definition, be "unholiness." Therefore, only as the Mishkan becomes functional, these concepts of separation and holiness come into focus, but like the scope of the book of Vayikra, the implications of these concepts reach every aspect of our lives and allow us to reach new levels of spiritual perfection.
For a more in-depth analysis see: http://arikahn.blogspot.co.il/2014/03/essays-and-lectures-parashat-shmini.html