“And that you may teach the children of Israel all the statutes which Yahweh has spoken to them by Moses.”
The idea here is that for anyone to come short of God's requirements is to be rendered unclean. Thus it is the duty of the priesthood to make all aware of God's statutes and requirements, both with regard to ritual and with regard to life. For to fall short of any would require cultic treatment in order to bring them back into a state where they can come to the Sanctuary and meet with God (that is partly what the guilt offerings were for). God's people must seek at all times to avoid all possible sources of defilement. They too must be holy
For us the question must always be, how can we ensure that we are the best for God? What should we avoid that might make us less than the best? In our case it is spiritual cleanness that we must encourage, and spiritual uncleanness that we must avoid (2 Corinthians 7:1 compare Mark 7:20-23). And we should be daily concerned that we do so. We must not enter His presence unclean.