A key to understanding certain Biblical passages is knowing about ancient concepts of ritual purity. Here is a verse that is a point of contention, for example:
Lev. 13:9-13 When the plague of leprosy is in a man, then he shall be brought unto the priest; And the priest shall see him: and, behold, if the rising be white in the skin, and it have turned the hair white, and there be quick raw flesh in the rising; It is an old leprosy in the skin of his flesh, and the priest shall pronounce him unclean, and shall not shut him up: for he is unclean. And if a leprosy break out abroad in the skin, and the leprosy cover all the skin of him that hath the plague from his head even to his foot, wheresoever the priest looketh; Then the priest shall consider: and, behold, if the leprosy have covered all his flesh, he shall pronounce him clean that hath the plague: it is all turned white: he is clean.
Skeptics have asked how a man is declared "clean" while being covered with leprosy. The context here as throughout Leviticus is ceremonial cleanness - not physical cleanness. Let's look at how the same word is used in other places:
Gen. 35:2 Then Jacob said unto his household, and to all that were with him, Put away the strange gods that are among you, and be clean, and change your garments...
Josh. 22:17 Is the iniquity of Peor too little for us, from which we are not cleansed until this day, although there was a plague in the congregation of the LORD...
2 Chr. 30:18 18 For a multitude of the people, even many of Ephraim, and Manasseh, Issachar, and Zebulun, had not cleansed themselves, yet did they eat the passover otherwise than it was written.
Proverbs 20:9 Who can say, I have made my heart clean, I am pure from my sin?
Of course there is in some contexts a relationship between physical and ritual cleanliness. But at the core of this and other passages lies rather a concept of ritual purity -- one which ties in to how the ancients viewed the world.
Our programmatic source for this essay is David Desilva's book, Honor, Patronage, Kinship and Purity [243ff]. This book is an excellent resource for understanding the thought-world of the Bible.
In ancient societies, purity codes "are a way of talking about what is proper for a certain place and a certain time...Pollution is a label attached to whatever is out of place with regard to the society's view of an orderly and safe world." It involves "drawing the lines that give definition to the world around us..." More than this: Purity in the ancient world "is fundamentally concerned with the ordering of the world and making sense of one's everyday experiences in light of that order, which is usually conceived as being a divine ordering of the cosmos..."
Ancient cultures like Israel's "draw extensive lines of purity, of clean and unclean, in an attempt to create a model of God's cosmic order and to help an individual locate his or her place in that order so that the person may know when pollution has been contracted and what needs to be done to dispel it, so that access to the holy God and his benefits will remain open." Breaches of boundaries are "unclean".
Hence the person partially leprous is ritually unclean; but the person who is totally covered with leprosy is ritually clean. Breaks in the skin or discharges likewise violate boundaries and are ritually unclean. From the Israelites food laws, something like a lobster which lives in the water, yet has legs, is ritually unclean because it breaks the boundaries between land and sea. Pilch and Malina [Handbook of Biblica Social Values, 24] also note the example of garments not being of mingled textiles (Lev. 19:19, Deut. 22:11).
If this seems odd, check yourself twice. First check the necessity of such thinking in the ancient world. As shown in Education in Ancient Israel by James Crenshaw, the ancients knew well that human society in their time was only a few steps away from anarchy and chaos. Constant reminders were needed, and constant vigilance, to protect the social order.
The interest in ritual purity represents a larger interest in the wholeness of the social order; maintaining order on one scale contributed to keeping order on a larger scale. "...[O]bserving these ordinances would be meaningful" for they "allowed the community of Israel to move in step with, or mirror, the divine order" and become "a living reflection of the character of the holy God in the midst of the world, a holy island of order in the midst of the Gentiles' aberrations."
Purity codes in other cultures serve similar purposes; all that is at issue is whose concept of order, if any, is true. Critics who live today with no visible threat of anarchy -- especially here in America -- simply don't appreciate life in such circumstances.
But check yourself again: You still may be a ritual thinker. In modern times you may think we have erased such concepts as these from our minds. Don't suppose that for a moment.
If you are a person who will not step on spittle on the sidewalk, or gets bothered when your vegetables spill over into the area of your plate where your meat is, you still maintain a form of this thought pattern -- trivial though it is. And those who maintain such patterns tend to reflect a larger sense of order in their lives.
Understanding Biblical concepts of purity is one of many keys to understanding the Bible as a whole.