I've heard plenty of Christians try to answer the why question by going back to the what. "You have to believe because Jesus is the Son of God." But that's answering the why with more what. Increasingly we live in a time in which you can't avoid the why question. Just giving the what (for example, a vivid gospel presentation) worked in the days when the cultural institutions created an environment in which Christianity just felt true or at least honorable. But in a post-Christendom society, in the marketplace of ideas, you have to explain why this is true, or people will just dismiss it.
Timothy KellerIf Jesus rose from the dead, then you have to accept all that he said; if he didn't rise from the dead, then why worry about any of what he said? The issue on which everything hangs is not whether or not you like his teaching but whether or not he rose from the dead.
Timothy KellerIt is no more narrow to claim that one religion is right than to claim that one way to think about all religions is right.
Timothy Keller