By Mark Dever
Mark Dever is the senior pastor of Capitol Hill Baptist Church in Washington, D. C., and the President of 9Marks. You can find him on Twitter at @MarkDever.
By Tim Keller
Tim Keller is senior pastor of Redeemer Presbyterian Church (PCA) in Manhattan, New York, and the author of numerous books. He is also co-founder and vice president of The Gospel Coalition. You can find him on Twitter at @timkellernyc.