Question: "What does the Bible mean when it says something is unclean?"
Answer: The Hebrew word translated “unclean” in Leviticus is used nearly one hundred times in this one book, clearly emphasizing “clean” status versus “unclean.” Animals, objects, food, clothing, and even people could be considered “unclean.”
Generally, the Mosaic Law spoke of something as “unclean” if it was unfit to use in worship to God. Being “clean” or “unclean” was a ceremonial designation governing the ritual of corporate worship. For example, there were certain animals, like pigs, considered unclean and therefore not to be used in sacrifices (Leviticus 5:2); and there were certain actions, like touching a dead body, that made a living person unclean and temporarily unable to participate in the worship ceremony (Leviticus 5:3).
Leviticus 10:10 taught, “You are to distinguish between the holy and the common, and between the unclean and the clean” (ESV). The parallel between “holy” and “clean” (and “common” and “unclean”) reveals that the command was related to one’s spiritual condition, though physical actions were often involved.
Certain foods were unclean for Jews and forbidden for them to eat, such as pork, certain fish, and certain birds. A skin infection could make a person unclean or unfit for presence at the tabernacle or even in the community (Leviticus 13:3). A house with certain kinds of mold was unclean. A woman was unclean for a period of time following childbirth. On holy days couples were restricted from engaging in sexual activity as the release of semen made them unclean until evening (Leviticus 15:18).
While a wide variety of circumstances could make a person, animal, or item unclean, the majority of the laws concerned activities disqualifying a person or animal in connection with the tabernacle offerings. An animal offered for sacrifice had to be without defect. The person who offered the sacrifice also had to be “clean” before the Law; i.e., the worshiper had to comply with the Law and approach God with reverence.
In the New Testament, Jesus used the idea of being “clean” to speak of being holy. In Luke 11:39–41 He says to the Pharisees, “Now then, you Pharisees clean the outside of the cup and dish, but inside you are full of greed and wickedness. You foolish people! Did not the one who made the outside make the inside also? But now as for what is inside you–be generous to the poor, and everything will be clean for you.”
“Clean” and “unclean” were concepts very familiar to those under the Old Testament Law. God called His people to separate themselves from the impurities of the world. The principle of being clean crosses into the New Testament as well, with the idea of living spiritually pure (2 Corinthians 6:17) and seeking to be holy, living a life worthy of our calling (Colossians 1:10).