Christ was met by the unclean men coming out of the tombs. These rock-hewn tombs were repulsive to the Jews and to dwell in them was deemed a sign of insanity. Because of the remains of the dead they contained, they were shunned by the Jews as unclean (Matthew 23:27). Under the Old Covenant, one could be physically defiled by touching a dead body. Even when a person died in a tent, the whole tent was regarded as unclean (Numbers 19:11, 14).
Unclean in Scripture means "to be defiled, polluted, unhealthy, or unfit," and refers to foods that are unfit, defilement of religious character, and moral or spiritual impurity. The word "defilement" describes a sinful and unfit condition (Isaiah 6:5). The Old Testament distinguishes between what is clean and helpful and what is unclean and unacceptable (Leviticus 10:10). The New Testament deals more with the spiritual application and lists uncleanness or moral defilement along with fornication and other sins as "works of the flesh" (Galatians 5:19-21).
In the gospels, "unclean" describes those who are possessed by demonic spirits through constant submission to evil. Uncleanness represents sin, and sin separates man from God. Because of sin, "we are all like an unclean thing" (Isaiah 64:6). Believers are not called to uncleanness but to live in holiness (I Thessalonians 4:7). We are not to yield our members to uncleanness but to righteousness and holiness (Romans 6:19).
The teaching about uncleanness springs from the concept of God's holiness (Leviticus 11:44-45). It is a miracle in itself that freedom from uncleanness and guilt is possible through God's grace. Holiness within, purity of heart, is possible through the exercise of faith in Christ's redemptive work and obedience to His truth.