There are several questions that fake Christians won't be able to answer. According to Tim Keller, these are questions that focus on hallmarks of a growing relationship with God.

Many times people think if God has called you to something, he's promising you success. He might be calling you to fail to prepare you for something else through the failure. | Timothy Keller Quote

The Gospel is good news not good advice. Advice = what we should do. News = report of what was done for us. | Timothy Keller Quote

Timothy Keller is the founding pastor of Redeemer Presbyterian Church in New York City, and a best-selling author of books like The Reason for God and Jesus the King.