Douglas Groothuis, a professor of philosophy at Denver Seminary, has been making the case for Christianity throughout his academic career. He heads the Christian Apologetics Master’s degree program at the seminary, he's written 16 books, and he podcasts at Truth Tribe, delivering a sharp message in a soft voice.

PW talked with Groothuis about his new book, World Religions in Seven Sentences: A Small Introduction to a Vast Topic (IVP, Sept.). In a chapter for each one, he examines a concept he considers fundamental to their worldview: Atheism: “God Is Dead.” Judaism: “I Am Who I Am.” Hinduism: “You Are That.” Buddhism: “Life Is Suffering.” Daoism: “The Dao That Can Be Spoken Is Not the Eternal Dao.” Christianity: “Before Abraham Was, I Am.” Islam: “There Is One God, and Mohammad Is His Prophet.” Spoiler alert: He gives his conclusion--that only Christianity proves fully true--on page 6: "While religions are many, truth is one; and all religions cannot be one, given their differing truth claims about the ultimate reality, humanity, morality, spiritual liberation, the afterlife, and more."

What drew you into apologetics? You say that you became a Christian when you were still in college, having studied philosophy and Eastern Religions. Why did you turn quickly to defending Christianity?

I tried to live a few months as a Christian just on blind faith, but that didn't work until I discovered apologetics with Francis Schaeffer's book The God Who Is There. It gave me the confidence that Christianity was meaningful, objectively true, and rational. God offers us eternal life through Christ and that's an important thing to know.

Your first books, (published in the 1980s and still in print), aimed to undercut New Age spirituality. Then came the wave of books by the so-called "New Atheists" such as Richard Dawkins, Sam Harris, and Christopher Hitchens. You open your World Religions primer with Atheism but move on quickly to other themes. Are the New Atheists old hat now?

The New Atheists are not as popular as 10 or 15 years ago. Back when there was a slew of books by them, they didn't offer any new arguments but they had a take-no-prisoners-attitude that made them popular. Today, I think people are looking more for entertainment or a therapeutic approach to life instead of a philosophical approach to the search for the ultimate meaning in life.

In America's religion marketplace, Buddhism seems to be gaining the most ground. However, you describe it as a "miserable system" for a hopeless life with no avenue for reform, renewal or resurrection. Why do you think Buddhism is so popular?

Buddhism has its precepts but a lot of people just appropriate the more therapeutic practices such as mindfulness, meditation, and quieting ideas and don't go further. These low commitments don't deal with Buddhism's primary idea that the only end to suffering is to escape the world.

In your book, Islam takes the sharpest hit. You describe Muhammad as immoral, treacherous, and vengeful and the Qur'an as "a hopeless message of salvation by good works offered to a terribly distorted idea of God." You advocate civility, noting " wouldn't offer a Muslim a glass of wine." How does your commentary on Islam square with your stated goal of "respectful disagreement"?

I try to write in such a way that a thoughtful person would take what I say seriously. We are in America, dealing with people of all different religious beliefs and commitments -- or none at all. It might help if people are more knowledgeable and conversant about them. There are elements of truth in all the world religions but only the full Bible — the Hebrew Bible and the New Testament — are uniquely true and true in a way that matters ultimately. This is the lens through which I understand other claims to truth.