“And that you may make a distinction between the holy and the common, and between the unclean and the clean,”
The next important point is the distinction between the holy and the common (the unholy), the clean and the unclean. This distinction will be taken up later in Leviticus in detail. But the point is being made by it that God is holy, and that nothing that comes short of that holiness is to be permitted into His presence. Nothing ritually unclean must enter the Sanctuary and its precincts, for it will defile it. So God enjoins that it is to be the responsibility of the priests to make the distinction and see that it is observed.
Uncleanness covers a wide variety of things and states, from differences between what may be eaten and what may not, and what may be touched and what may not, to bodily imperfections and discharges, to uncleanness resulting from contact with death, and so on, to uncleanness caused by disobedience to God's commandments, and such uncleanness must be removed before men enter the Sanctuary. For God is holy, and it is the priest's duty to discern whether men are clean or unclean, and to instruct them on all such matters so that they may themselves discern their own state. The stress is on the importance of keeping the Sanctuary and its precincts holy so as to bring home the holiness of God. It meant that the concern for holiness would become a daily concern for all the people, both physically and morally.