At American Vision, Gary DeMar explains more clearly than I could why Christianity is a necessity for good morals.
“So what is the basis for law?…Ultimately, where does morality find its justification, its jurisdictional legitimacy? Every person approaches an ethical norm with a prior commitment to some fundamental interpretive principle. No one is commitmentless. No one approaches anything in a neutral way. There is no agreed upon definition of reason or what’s reasonable.”
If Jesus Christ is really king, then all people (as well as all things) are either for Him or against Him. All laws are either conformed to His authority or opposed to His authority.
“What is the basis for morality given material-only assumptions about reality? This approach is a dead-end. R.C. Sproul writes that ‘God’s existence is the chief element in constructing any worldview. To deny this chief premise is to set one’s sails for the island of nihilism. This is the darkest continent of the darkened mind—the ultimate paradise of the fool.’ ”
It is impossible to develop a system of thought without God (or a god). Even atheism is faith that there is no God, which amounts to faith in your reasoning ability to determine that very fact. But the person who tries to construct a system of values, if the values are moral, must borrow them from Christianity. It’s like a cook who wants peach cobbler but doesn’t believe in growing peaches. His only alternative is to steal the peaches from his neighbor’s orchard. People want biblical morals in society, but until they bow before Jesus Christ as Lord, they will have to “steal” godly morals from Christians.