Though sometimes conflated, purity and holiness aren’t the same thing in the Old Testament. There are two overlapping spectra: A spectrum from profane or common on the one side and holiness/sanctity on the other, and a spectrum with unclean/impure to clean/pure on the other.
The difference is evident in the Hebrew. The word tame’ refers to impurity; it is both a verb (become unclean) and a noun (the status of “unclean”). One can become tame’ by touching a carcass of an animal (Leviticus 5:2), eating unclean food (11:8), having skin disease (13:11, 15, etc.), suffering various forms of discharge from the genitals (15:2, 25-26), giving birth (Leviticus 12), or being in the presence of a human corpse (Numbers 19:13).
The opposite of tame’ is taher (verb, “become clean” or “pronounce clean”) or tahorah/tohar (noun, “purity” or “purification”). Impure things are purified when put into water until evening (11:32), or through a waiting period followed an offering (women after childbirth, 12:7-8), by washing body and clothes and receiving the declaration of clean from a priest (13:6; 15:13, 28), or being sprinkled with special water of purification (19:12, 19). Some rituals of purification, such as those from skin disease or childbirth, are complex. Others are quite simple. It’s a priest’s job to distinguish between the tame’ and the tahor (Leviticus 10:10).
Through the ritual of taher, the person is transferred into a state of cleanness, tohar. Impurity happens naturally. Purity is a state achieved by following a prescribed ritual.
Holiness is described with various forms of the word qadash. This too functions both as a noun, describing persons, places, objects, and as a verb, meaning “consecrate” or “sanctify.” Things and people are consecrated by being set apart as Yahweh’s own (the firstborn, Exodus 13:2), by rituals of consecration that include washing (Exodus 19:10, 14), by rituals of ordination (Exodus 28:3, 38, 41; 29:1; Leviticus 8:10-12, 15) or by rituals of consecration (Exodus 29:36-37).
Yahweh Himself consecrates His house and His priests (Exodus 29:44) and consecrates the holy place by coming near in his glory (Exodus 29:43). Set apart by Yahweh’s presence, Israel is to remain consecrated to Yahweh (11:44; 20:7), partly by avoiding ritual defilements (11:44).
The opposite of qadash is chol (Leviticus 10:10). At times, this simply refers to a state other than a state of holiness. At other times, it can refer to a violation of holiness. Idolatry causes “profanation” (18:21; 19:12) and so does sexual sin (19:29). The form chalal is used of offenses against holy things (Leviticus 19:8) or persons (21:4, 6, 9, 12, 15).
Though distinct spectra, the two concepts are interrelated. Defilement only occurs in proximity to holy places and things. Before Israel came to Sinai, Yahweh doesn’t live in their midst; there’s no tabernacle, no singular altar or holy place. Once that tabernacle is set up, and Yahweh moves in, the place becomes holy, and access to that holy place, even in the court, requires ritual purity. The first hint, for instance, that God’s presence requires sexual abstinence occurs at Sinai (Exodus 19).
They are similar also in the fact that both spectra are “graded” systems. As Leviticus 15 indicates, some forms of impurity (from sexual intercourse, for instance) do not spread to others. Other forms of impurity (menstruation) defile things and other people. Some things are simply impure. Other things are “mothers” of impurity.
In Purity, Sacrifice, and the Temple, Jonathan Klawans offers a helpful discussion of this distinction, though he uses the terms “ritual” and “moral” impurity. The two differ at a number of points.
Ritual impurity is the result of natural processes and social life. As Klawans summarizes, “Birth, death, sex, disease, and discharge are part of normal life. Ritual impurity is also generally unavoidable. While certain defiling substances are relatively avoidable (e.g., touching carcasses), discharge, disease, and death are inescapable. Some ritual impurities are not just inevitable but obligatory. All Israelites (priests included) are obligated to reproduce (Gen. 1:28, 9:7). All Israelites (except the high priest) are required to bury their deceased relatives (Lev. 21:10–15; cf. 21:1–4). Priests are also obligated to perform cultic procedures that leave them defiled as a result (Lev. 16:28; Num. 19:8)” (54).
There is no sin involved in ritual impurity, though it is a sin to refuse or neglect to perform the rites of purification or to enter the sanctuary of Yahweh in an impure state. Ritual purity can be contagious, and it lasts for varying lengths of time, but is never permanent (54).
Moral defilement, by contrast, is sin: “Moral impurity results from committing certain acts so heinous that they are considered defiling. Such behaviors include sexual sins (e.g., Lev. 18:24–30), idolatry (e.g., 19:31; 20:1–3), and bloodshed (e.g., Num. 35:33–34). These ‘abominations’ bring about an impurity that morally—but not ritually— defiles the sinner (Lev. 18:24), the land of Israel (Lev. 18:25, Ezek. 36:17), and the sanctuary of God (Lev. 20:3; Ezek. 5:11). This defilement, in turn, leads to the expulsion of the people from the land of Israel (Lev. 18:28; Ezek. 36:19)” (55).
In contrast to ritual defilement, moral defilement doesn’t exclude a person from the sanctuary (partly because it is undetectable), though it does defile the sanctuary: “Since moral impurity does not produce ritual defilement, sinners—in contrast to those who are ritually impure—are not excluded from the sanctuary. In the case of the suspected adulteress (Num. 5:11–31), the woman is brought into the sanctuary itself in order to determine her moral status. It also appears that Israelite murderers sought sanctuary in the sanctuary (Exod. 21:14; cf. 1 Kgs. 1:50–53 and 2:28–30). Moral impurity does indeed defile the sacred precincts (e.g., Lev. 20:3). But the effect of moral impurity does not penetrate the holy realm by the entrance of sinners into it. Moral impurity is a potent force unleashed by sinful behavior that affects the sanctuary even from afar, in its own way” (55).
Moral impurity defiles because of the sanctuary but it registers on the holy land, the land Yahweh has claimed for His own, the land where He dwells. There are no rites of cleansing for land defilement. God alone can cleanse, by sweeping Israel away.
Again terminology provides a clue to the distinct areas of concern. Tame’ is used both for ritual and for moral defilements. It is commonly used for the sorts of natural processes that cause ritual defilement, but it is also used to describe the effect of morally defiling sins. A man who commits adultery is “defiled” with her (18:20), and bestiality is also a defilement of the person (18:23). The land becomes defiled by sexual sin and idolatry (18:27-28), and that is a danger because it was the defilement of the land with these sinful practices that caused the land to drive the Canaanites out.
Some terms, though, are used only of moral defilement. Blood shed on the land “pollutes” (chaneph) the land (Numbers 35:33; Psalm 106:38), and other sins also pollute the land (Isiaah 24:5). “Abomination” (to’evah) is also used specifically for defilements of the land, especially for sexual sins and idolatry (Leviticus 18:22, 26, 27, 29-30; 20:13). Abominations cause the land to vomit the inhabitants.
Klawans’s terminology is misleading, I think, because the ritual regulations were not amoral, automatic rituals. Leigh Trevaskis (Holiness, Ethics, and Ritual in Leviticus) has argued that the rituals symbolized moral faults. Rituals were part of a pedagogy that is not simply liturgical, but provided a guide for the life of the covenant people in general.
Forbidden foods, for instance, are not arbitrarily chosen but teach Israel what kinds of things they are to avoid taking into their lives. The word “belly” in Leviticus 11:42 is used elsewhere only in Genesis 3:14, where it describes the serpent’s mode of locomotion. Unclean animals are serpent-like creatures, and Israel, the new Adamic people, is to refuse to eat those animals that represent the serpent.
Leviticus 13:2 makes an unusual reference to an adam who contracts skin disease, a reference, Trevaskis argues, to the original adam in the garden. As Jacob Milgrom argued, we are dealing with “death,” but not in the physical sense; we are dealing with death as exclusion from God’s presence. In the laws of skin disease, the focal point of uncleanness is the exposure of flesh. “Live flesh” is “explicitly identified as unclean” in 13:14-15, and when the underlying flesh is completely covered with skin disease, the person is clean. Trevaskis notes that skin disease is often described with the word “stroke,” suggesting that Yahweh has smitten the person.
Overall, the laws symbolically depict “human rebellion under divine judgment,” an exposure of flesh that God “strikes” with fire or wound. Skin disease incarnates God’s judgment on “flesh.” No wonder the skin-diseased person has to engage in five practices that symbolize his entry into the realm of death, “exclusion from God’s immediate presence.”
In Leviticus 15, exposure of flesh is like exposure of nakedness in God’s presence: “While ‘one flesh’ lives happily in God’s presence within the Garden of Eden, it is the object of divine punishment in Genesis 6–9. . . . we may speculate that God’s immediate presence is no longer accessible to ‘naked flesh’ in the way it was in the Garden.”
This moral dimension to the purity rules is the foundation for Paul’s appeal to purity and holiness rules in framing exhortation to Christians. That is not a departure from Torah but a fulfillment.