God made it clear to Moses, and through him to the people of Israel, that those who would abide by his covenant are expected to live a different kind of life from people who do not believe in God. He did so by setting out the code of Old Testament law, which we call the Ten Commandments, or the Decalogue.

Not only did God address this word to the ancient Israelites, expecting them to observe it, but modern Jews and Christians, too, are to respect God’s laws and live lives that are "holy and acceptable to God." That, indeed, is a large order. Is there anyone who can keep all ten commandments perfectly? Hardly. But it is God’s will that his covenant should be respected and obeyed by all those who claim to believe in him.

What Romano Guardini writes in his The Saints in Daily Christian Life…