The sight of blood sets off shrill alarm bells in the human soul. Most people today connect blood with emergency and danger: death, disease, the carnage of battle. In some places, though, blood still carries another meaning entirely: mastery and power. Think of the terrorist standing at the window of a police station in Ramallah in late 2000, waving his hands covered with the blood of the unarmed Israeli reservist whom he has just murdered, to the cheers of the mob below.

In the ancient world, drinking blood was a common element of idol worship. Judaism, starting with the Bible, has always gone in the opposite direction. Human beings are told repeatedly not to eat blood—a ban first conveyed to Noah in Genesis 9:4, repeated by Moses in Deuteronomy, and heard most often in this week's reading. An animal killed for food must have its blood completely drained and covered with earth. As Rabbi Jonathan Sacks has pointed out, the Bible connects the eating of blood directly with other idolatrous practices—and specifically with human sacrifice. In both cases, God says He will "set My face against" anyone who breaks His law.

Over the centuries, Jewish tradition has carried this anti-blood message even farther. While the biblically mandated sacrifices included the sprinkling of blood on the altar, the prayers that would come to replace Temple sacrifice rarely mention this part of the ritual. The process of "koshering" meat involves salting it to make sure not a drop of blood remains. Historically, rituals involving blood, including the slaughtering of animals or circumcision, became relegated to isolated professions, and were often performed by the same person. Tellingly, discussions of matrilineal descent—according to which anyone born to a Jewish mother is a Jew—are devoid of any reference to blood as a source of cultural identity. Jews have no "bloodlines," "blood covenants," or "blood brothers."

The reason? In this week's portion, the Bible is explicit about it: "For in its blood is the life of all flesh, and on it depends its life" (Leviticus 17:14). The same logic is repeated several times, phrased as a compelling, self-sufficient argument. But what does it really signify?

Deep inside us, blood symbolizes physical life—the sheer mystery of it. If we are fortunate, we spend most of our days happily ignoring this mystery. But when faced with key moments of emergency, especially sickness and death, we are reminded of our place in the universe, of the ungraspable miracle that life really is. The sight of blood tells us that our lives are not finally under our control. Blood humbles us.

In drinking blood, ancient peoples sought to replace mystery with mastery. Proclaiming their domination over the deepest questions of existence, they asserted their self-confidence (or, some would say, betrayed their anxiety) by arrogating to themselves infinite license, up to and including the sacrifice of their own children on the altar of their gods.

Nor is this blood-arrogance limited to the ancient world. The twentieth century was notorious for ideologies claiming authority over all of life, even over nature. Waving the red flag or shouting fiery slogans of blood-and-soil, acolytes of these ideologies terrorized vast swaths of the earth and murdered untold millions—all in order to show that they, not God, held the reins of life and death, and were fit objects of worship.

By now we need not ask where such thinking leads. The contrary message of the Bible, with its unequivocal ban on blood, is to treat the miraculous gift of life with respect and awe—"for in its blood is the life of all flesh."

David Hazony's first book, The Ten Commandments: How Our Most Ancient Moral Text Can Renew Modern Life, will be published by Scribner this coming September.