Fausset's Bible Dictionary
Unclean and Clean
(See Leviticus 20:25-26; Leviticus 17:3-11; Leviticus 7:27. The ground of the distinction was Israel's call to be Jehovah's peculiar people (Deuteronomy 14:21). Their daily meals should remind them of the covenant which separated them from the whole Gentile world as holy unto the Lord. The clean animals answer typically to God's holy people, the unclean to the idolatrous Gentiles. So Peter's vision (Acts 10:11-15) of the "sheet bound by four (the number for worldwide extension) rope ends (archais , Alford) containing all kinds of four footed beasts, creeping things and fowls," of all which he was commanded to eat, was the appropriate type of the abolition of distinction, not only between meats (compare 1 Timothy 4:4; Matthew 15:11) but between Jew and Gentile. Henceforth, "the kingdom of God is not meat and drink, but righteousness, peace and joy in the Holy Spirit" (Romans 14:17).; LEPER; RED HEIFER.) See Leviticus 11;
The distinction had regard, not to living, but to dead animals. The Israelite treated his unclean camel and donkey as carefully, and came into contact with them as often, as his ox or sheep. Every dead body, whether of man or beast, dying or killed in an ordinary way, was unclean. Thus the grand opposition between life (connected with holiness) and death (connected with sin) is marked. By slaughtering in a prescribed manner, pointing to the antitypical Deliverer from sin and death, animals became exempted from the uncleanness attached to death. The blood in which is "the life of the flesh" being drawn off from the meat, the latter by being presented before Jehovah became clean as food for Jehovah's people by His gift. The ruminating quadrupeds, fish with fins and scales, gallinaceous birds and such as feed on vegetables, and not the raptores and carnivorous; those not revolting to our instincts; those affording the most wholesome foods: all these were the foods chosen as typical symbols of Israel's separation, from moral uncleanness, to Jehovah.
Unlike the Egyptian law intended for the priests alone, or the Hindu law binding only on the twice born Brahmin, or the Parsee law for those alone disciplined in spiritual matters the Mosaic law was for all, Israel being "a kingdom of priests, an holy nation" (Exodus 19:6), foreshadowing our Christian high calling, ministers and laymen alike (1 Peter 2:9; Isaiah 61:6). The animal kingdom teaches ethical lessons. The cloven hoof, standing firmly on the ground yet adapted for locomotion, figures the believer's standing and walk in the world. Rumination symbolizes due meditation on and digestion of God's law (Joshua 1:8; Psalms 1:2). The fish's fins raise it out of the mud where the eel dwells; so do prayer and faith raise the soul out of darkness and uncleanness. The decree of the Jerusalem council (Acts 15:20-21) rested simply on the desire to avoid offending needlessly the prejudices of Jews and Jewish Christians, "for Moses of old time hath in every city them that preach him."
Mercy to the beasts pervades the law. Though it could not injure the mother to boil the dead kid in the mother's milk, yet it was forbidden, as the milk was the kid's "life" and had a relative sanctity resembling that of forbidden blood (Juv. xi. 68); the delicate feeling of the sentiment would suggest, general humanity toward brutes. Swine are liable to disease from foul feeding, and in Palestine are not very wholesome food; so also fat and blood; but the spiritual reason of prohibition was the main one, the swine's uncleanness of feeding typifying moral impurity, and the fat and the blood being God's exclusive perquisite for sacrifice on the altar. Uncleanness cut one off for a time from his social and religious standing among God's people. The Old Testament divine law invested the human body with a sanctity which shadowed forth the holiness required of the whole man, "spirit, soul, and body" (1 Thessalonians 5:23): hence, flows the frequent addition to the several ceremonial precepts, "I am the Lord your God," "ye shall be holy, for I am holy" (Leviticus 11:44-45).
The Lord's mark of ownership, circumcision, was on them; and that ownership appeared in every ordinary act of life, the antitype to which is our New Testament rule (1 Corinthians 10:31; 1 Peter 4:11; Colossians 3:17). Three degrees of uncleanness may be distinguished. (1) That lasting until even, removable by bathing and washing the clothes; as contact with dead animals. (2) That lasting seven days, removable by the "Water of separation," as defilement from a human corpse. (3) From the diseased, puerperal, or menstrual state; lasting as long as this continued; in the leper's case, for life. As blood shedding typified the deadliest sin, so washing typified cleansing from this (Deuteronomy 21:6-8; Psalms 26:6; Psalms 73:13; Isaiah 1:15). Man's passage into, and out of, his mortal state was connected with ceremonial pollution, marking his inherent corruption; the mother of a male continued unclean 40 days, of a female 80 days (Leviticus 12:2-5): the difference representing woman's being first in the sin and curse (Genesis 3:16; 1 Timothy 2:14).
For the cases of male, female, and intersexual defilement, all handled in holy writ with reverend decorous purity, compare Leviticus 12; 15; Leviticus 20:18. All these detailed rules, by a broad margin, separated purity from impurity. The touch of those unclean by contact with a dead body imparted defilement (Numbers 19:22; Haggai 2:12-13). "Holy flesh" (that of a sacrifice) makes holy the skirt in which it is carried; but that "skirt" cannot impart its sanctity to anything beyond, as bread (Leviticus 6:27), implying a sacrifice cannot make holy the disobedient. An unclean thing imparts its uncleanness to anything, whereas a holy thing cannot confer its sanctity on the unclean (Numbers 19:11; Numbers 19:13; Numbers 19:22). The law of uncleanness until even, after the conjugal act, would discourage polygamy and tend toward the health of parent and child.
So as to involuntary self pollution the restraint would be medically and morally salutary. All animals that were unclean to touch when dead were unclean to eat, but not conversely; all unclean to eat were unclean to sacrifice, but not conversely. A garment or vessel became unclean by touch of a carcass of an animal unclean for food; it must be purified by washing. So the ashes of the red heifer, the remedy for uncleanness, themselves defiled the clean (Numbers 19:7, etc.); Deuteronomy 23:10-13 directs as to impurities of a host encamped before "enemies" (Deuteronomy 23:14); God's presence in the host is made the ground of avoiding every such pollution. How different from worldly camps, where the ordinary rules of morality and religion are so often relaxed! The defilement by touch of a leper or person with an issue shows the inherent holiness of Jesus, who, so far from being defiled by the leper or the woman with the blood issue, removed their defilement.
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Fausset, Andrew R. Entry for 'Unclean and Clean'. Fausset's Bible Dictionary. https://www.studylight.org/dictionaries/eng/fbd/u/unclean-and-clean.html. 1949.