Definition and Context
Uncleanliness, in biblical terms, refers to a state of ritual impurity that prevents individuals from participating in certain religious activities and ceremonies. This concept is primarily rooted in the Old Testament, where it is extensively detailed in the Mosaic Law. Uncleanliness can result from various sources, including certain foods, bodily discharges, skin diseases, and contact with dead bodies.

Sources of Uncleanliness
1. Dietary Laws: Leviticus 11 outlines the dietary restrictions given to the Israelites, specifying which animals are considered clean and unclean. For example, Leviticus 11:7-8 states, "And the pig, though it has a divided hoof, does not chew the cud; it is unclean for you. You must not eat their meat or touch their carcasses; they are unclean for you."

2. Bodily Discharges: Leviticus 15 addresses various bodily discharges that render a person unclean. Verses 2-3 state, "When any man has a bodily discharge, the discharge is unclean. This uncleanness is due to his discharge, whether his body allows the discharge to flow or blocks it."

3. Skin Diseases: Leviticus 13-14 provides detailed instructions on diagnosing and dealing with skin diseases, often translated as "leprosy." Leviticus 13:3 says, "The priest is to examine the sore on his skin, and if the hair in the sore has turned white and the sore appears to be deeper than the skin of his body, it is a leprous sore. When the priest examines him, he must pronounce him unclean."

4. Contact with the Dead: Numbers 19:11 states, "Whoever touches any dead body will be unclean for seven days." This law underscores the seriousness of death-related impurity and the need for purification rituals.

Purification and Restoration
The process of purification from uncleanliness often involved washing, waiting periods, and sometimes sacrifices. Leviticus 14:19-20 describes the ritual for cleansing a person healed from a skin disease: "Then the priest is to sacrifice the sin offering and make atonement for the one to be cleansed from his uncleanness. After that, the priest shall slaughter the burnt offering and offer it on the altar, together with the grain offering, to make atonement for him, and he will be clean."

New Testament Perspective
In the New Testament, Jesus and the apostles addressed the concept of uncleanliness, often emphasizing the internal over the external. Mark 7:18-23 records Jesus' teaching: "Are you still so dull? He asked. Do you not see that nothing that enters a man from the outside can defile him, because it does not enter his heart but his stomach, and then it is eliminated? (Thus all foods are clean.) He continued: What comes out of a man, that is what defiles him. For from within the hearts of men come evil thoughts, sexual immorality, theft, murder, adultery, greed, wickedness, deceit, debauchery, envy, slander, arrogance, and foolishness. All these evils come from within, and these are what defile a man."

Theological Implications
Uncleanliness in the Bible serves as a symbol of sin and the separation it causes between humanity and God. The laws of uncleanliness highlight the holiness of God and the need for His people to be set apart. The New Testament shifts the focus from ritual purity to moral and spiritual purity, emphasizing the transformation of the heart through faith in Christ.