Say to them [i.e. the "cohanim"; English: the priests], "If any one of all your offspring throughout your generations approaches the holy things that the people of Israel dedicate to the Lord, while he has an uncleanness, that person shall be cut off from my presence: I am the Lord." (Vayikra / Leviticus 22:3; ESV)
So much of this third book of Moses is concerned with two pairs of concepts: clean and unclean, holy and common. These concepts are foreign to many of us. Even religious and spiritual people have little understanding of the Torah's perspective on such things. Many of us tend to make a distinction between the "sacred" and the "secular" as if there are some aspects of life that are separate from God and his influence. The Torah and the rest of the Bible make no such distinction. Since the God of Israel is the creator of all things, he is also the King and Judge of all things. Because all life exists under his domain, his people are called to live all of life in service to him.
Yet there are distinctions that God does make. He distinguishes between the clean and the unclean, the holy and the common. The terms clean and unclean (Hebrew: tahor and tamei) describe the state of a thing or person in relationship to their acceptability within the community of the people of God, especially with regard to God himself. The unclean is not acceptable in God's presence and must not be tolerated as part of the normal life of the community. In fact that which is unclean can contaminate that which is clean. Much care was to be taken to ensure such contamination would not occur.
The holy and common (Hebrew: kodesh and chol) are another pair of concepts that describe distinctions God makes. Unlike clean and unclean that refer to a state of acceptability, holy and common refer to the distinction between that which has been specially separated to God for his use and that which is not. These concepts are not concerned about whether or not something or someone is good or bad. It is simply a way to distinguish between that which is set aside for God's use and that which is not.
While these two pairs of concepts describe different aspects of life, how they interact with each other is crucial. That which is holy must also be clean. Since God will not tolerate uncleanness in his presence, there is dire consequences when something or someone who is holy becomes unclean.
This is the lens by which we need to see the world. Human beings were created by God to be his representatives on earth. We were deemed both clean (acceptable as members of his community) and holy (set apart for his service). Our first parents' rebellion against God made them unclean. Since they who were holy became unclean, they and all humanity after them were cast out of God's presence.
Unless we come to grips with the human condition as God sees it, we will never be what God intended. Denying it, medicating it, or covering it up through hard work or the pursuit of pleasure will never restore us to the fullness of being the children of God we were meant to be.
The story of the Bible is the story of God's plan to cleanse (make acceptable) humanity in order that we might once again be holy (set apart to serve him). That is why he chose Abraham and his descendants culminating in the coming of the Messiah. Messiah's life, death, resurrection, and ascension restore those who follow him to the state and function for which we were originally designed.
As we see life through the lenses of clean and unclean, holy and common, we will see our lives as God does. Not only will we become what we were meant to be, but we will also begin to relate to others and to the things of life as they were meant to be as well.