NOTES for Lev 8:1-36
Before priests began their service, they had to be specially sanctified. The point was not that God had some special holiness for them, inaccessible to others; the point lay in the very meaning of priestly ministry. God conceived His people as a people-community, expecting that every member of it would be sanctified by God's presence, the same presence that was first revealed to Moses at Sinai and then accompanied the people throughout their historical path.
It turned out, however, that the people were not ready for such a life: most Jews were afraid to remain one on one with God; they preferred that leaders, special people chosen by God specifically for such direct communion, communicate with Him. Seeing this, God meets the people halfway and establishes the institution of the priesthood. The meaning of the priesthood is that among the people there would always be a certain community of people who are constantly sanctified and always remain in God's presence.
Ideally, everyone should have lived this way, but in reality this was impossible, and then God separates from the people a certain part that will remain at the altar constantly, though it itself will not be constant: the priests serving at the Tabernacle, and later in the Temple, replaced one another, so that each time they began their service, they had to go through special rituals of cleansing and dedication. Still, at the altar there was always a certain, comparatively small, community that remained sanctified: a priest on duty was not allowed even simply to leave the courtyard until the days of his service were completed, whether it was the courtyard of the Tabernacle or, later, of the Temple.
He, the serving priest, had to remain physically in God's presence at all times, preserving the state of sanctification until the days of his service were completed. The greater part of the people, however, was sanctified periodically, some weekly, and some only a few times a year: in Yahwism there were only four great obligatory feasts in the year, and at those participation in the sacrifice was obligatory.
Those who came to the altar weekly were people of real faith, for whom their faith was not a mere formality, as it often was for the majority. Yet even they still could not preserve the state of holiness constantly: then, at the beginning of the spiritual path, no one yet knew how to preserve it and not lose it. Thus there were always sanctified people living in God's presence among the people, but they were a minority. For the majority, sanctification was a temporary and passing state.