According to the Bible, the Ten Commandments were a covenant between God and the Israelites: You promise to follow my rules, God said, and I'll promise to show mercy on you. By then, the Israelites had endured four centuries of servitude, followed by several decades of walking south through an inhospitable desert. "I am the Lord thy God, which have brought thee out of the land of Egypt, out of the house of bondage," God reminded them.

The Ten Commandments, also known as the Decalogue, first appear in the Bible in Exodus 20, and then again in Deuteronomy 5. In neither Exodus nor Deuteronomy are the commandments numbered, nor are they clearly delineated, so not all religions number them the same way. Jews, Roman Catholics and most Protestants, for example, disagree on which verses to include in the first commandment.

The Decalogue is two sets of laws: The first four require a relationship with God; the second six dictate behavior between people. Those six rules are standard moral prescriptions, even for what we might consider fairly barbaric times. "They were a very normal, very early, primitive first step toward the development of a legal system and a moral system," notes Prof. John Witte, director of the Center for the Study of Law and Religion at Emory University in Atlanta.

In short, they're a start.

"To have left rape and child abuse and genocide and slavery out of the account is to have been negligent in some degree, even by the lax standards of the time," as writer Christopher Hitchens observed in a 2003 article in the online magazine "Slate."

By the time Jesus was offering his own commandments and Beatitudes a millennium later, the to-do list had evolved to include a commandment about love and a list of virtues that highlighted mercy and humility. It's the difference between the "morality of duty" and the "morality of aspiration," Witte explains.

For early Roman Catholics, the Ten Commandments were important as moral signposts, but so were the Seven Sacraments — baptism, Eucharist, reconciliation, confirmation, marriage, holy orders and anointing of the sick.

Later, Protestant reformers looked for something else, besides the sacraments, on which to base their legal and moral systems, Witte says. "In rejecting that (Catholic) sacramental theology, they were looking for an alternative, biblically grounded foundation, and the foundation on which they seized was the Decalogue."

So, for Protestants, the Ten Commandments were "the road map for what the law should be," says Professor W. Cole Durham, director of the International Center for Law and Religious Studies at Brigham Young University. "Melancthon, the great Protestant scholar at the time of the Reformation, founded criminal law on the commandment 'thou shall not kill,' and property law on the commandment 'thou shall not steal,"' and so on, Durham says.