In the Old Testament times, God gave Israel an inviolable set of commandments when the Mosaic law was established. This was to make Israel “set apart” for God as its people entered into a covenant with Him. Part of these commandments was the distinction between the clean and unclean, as written in Leviticus 10:10:
“And that ye may put difference between holy and unholy, and between unclean and clean.”
The Mosaic law was very specific in the distinction of what is unclean. The Israelites followed very strict dietary rules as to what animals were allowed for them to eat or use for sacrifice before God – pig, camel, hare, raven, eagle, any seafood without scales, and many others – and this can be found in the whole chapter of Leviticus 11. There are also certain physiological conditions that can make a person temporarily unclean, such as a woman’s childbirth (Leviticus 12), serious skin diseases (Leviticus 13-14), a woman’s menstrual period (Leviticus 15:19-24), a man’s emission of semen (Leviticus 15:16-17), sexual intercourse (Leviticus 15:18 The woman also with whom man shall lie with seed of copulation, they shall both bathe themselves in water, and be unclean until the even.), a woman’s bleeding beyond her menstrual period (Leviticus 15:25-30), and other bodily discharges (Leviticus 15:2-15). Lastly, other external factors were also considered unclean, such as a house or clothing contaminated by mold or mildew (Leviticus 13:47-59), touching the carcass of a dead animal (Leviticus 5:2 Or if a soul touch any unclean thing, whether it be a carcase of an unclean beast, or a carcase of unclean cattle, or the carcase of unclean creeping things, and if it be hidden from him; he also shall be unclean, and guilty.), touching a dead human body (Numbers 5:2, 19:11), and coming in contact with someone who is considered unclean (Leviticus 15; 22:4-7; Numbers 19:21-22).
The distinction between what is “clean” and “unclean” is purposefully for the sake of knowing which are ceremonially inadmissible for worshipping God. Since God’s people are to be holy or set apart for God, and they are giving worship to a holy God, they must strictly comply with what is required in reverence to the Holy One of Israel. Non-compliance to these laws can render a person unfit to present his or her offerings before God in the tabernacle. But there are also provisions in the Mosaic law for those who have found themselves to be unclean that if met properly, can make them ceremonially clean again. Though the rigid requirement to avoid what is unclean may seem to appear merely external, they have spiritual and practical implications, such as the law forbidding an Israelite from eating pork, for instance. In Old Testament times, the pagan nations surrounding Israel use these unclean animals, such as pigs, for ritual sacrifice to their gods, and God does not want His people to have any reason to have fellowship or participate in the idolatry of these heathens. You see, God does not just establish laws for no reason at all. He wants His people to be different from the rest of the idolatrous world, for He values them greatly.
In the New Testament, Jesus redefines the idea of clean and unclean. He taught about the real significance of what makes a man unclean in Mark 7:14-23. It is not the physical or external “uncleanness” that makes a person unclean, but the internal filthiness of a person’s heart that defiles him or her—the sinful thoughts, desires, and intentions. One can be seen as externally or ceremonially clean as one perfectly follows all the requirements of the law, but because of the utter sinfulness of the heart, being clean and fit to come into the presence of God is impossible for any man. That is why forgiveness, redemption, and purity come to a person only through faith in the blood of Jesus. As one follows Christ, we must rid ourselves of the filthiness of sin and no longer conform to the unclean patterns of the world. We must allow Jesus to transform our whole being into His likeness (Romans 12:2 And be not conformed to this world: but be ye transformed by the renewing of your mind, that ye may prove what is that good, and acceptable, and perfect, will of God.) and be mindful that our body is now the temple of the Holy Spirit, to be used only for what brings glory to our God.
“But if we walk in the light, as he is in the light, we have fellowship one with another, and the blood of Jesus Christ his Son cleanseth us from all sin.”
(1 John 1:7 KJV)