Let me explain. G. K. Chesterton, the famous British writer, was once invited to a meeting of the leading intellectuals in England. They were asked if they were shipwrecked on an island, what would be the one book they would want to have with them. Everyone expected Chesterton, a prominent Christian, to say “the Bible.”

When it came his turn to speak, however, Chesterton said that if he were shipwrecked on a desert island, he’d like to have “Thomas’s Guide to Practical Shipbuilding.”

The point is that oftentimes we need to understand things that are not covered in the Bible. And we need to understand things that help us apply biblical teaching to all of life. This is why I teach biblical worldview.

A man once told Oswald Chambers that he read only the Bible. Here’s what Chambers replied:

“My strong advice to you is to soak, soak, soak in philosophy and psychology, until you know more of these subjects than ever you need consciously to think. It is ignorance of these subjects on the part of ministers and workers that has brought our evangelical theology to such a sorry plight…The man who reads only the Bible does not, as a rule, know it or human life.”

And when it comes to making a biblical case on any hot topic — taxes, the deficit, homosexuality, whatever — we need to understand the issue and how to make that case in a way that is accessible to believers and non-believers alike.

Brit Hume, Robby George and I have just released a DVD teaching series on ethics called Doing the Right Thing. It’s one of the most important projects I’ve undertaken in my ministry. You can get it at ColsonCenter.org. Every principle we teach on ethics is biblically based. But rarely did we cite the Bible as authority. This is because this ethics course, we believe, will be taught in secular colleges and business schools — as well as in churches and small groups. So, it’s got to be accessible to everybody.

The sad fact is that today, starting a conversation with “the Bible says” will often cause the listener to stop listening. So what you do is make arguments based on what the Reformers called common grace, or what historically has been called natural law.

This is what Paul did when he gave his famous sermon at Mars Hill, his first foray into the Greek culture. He quoted Greek poets; he referred to Greek artifacts. He thoroughly engaged their culture. And then he used their beliefs to lead directly into the gospel.

This is why we must study biblical worldview, to compare how the Bible works out in life versus how other systems of thought do. I assure you: You will see that the biblical way is the only way to make sense of the world, to live rationally in the world, and eventually, your friends will see this as well.