Mike Cosper is the director of the Harbor Institute for Faith and Culture, where he works to create resources for Christians living in a post-Christian world. Prior to that, he was a founding pastor at Sojourn Community Church in Louisville, Kentucky, where he served for sixteen years as the pastor of worship and arts. TIMOTHY KELLER is founder and pastor of Redeemer Presbyterian Church in New York. He is the best-selling author of The Prodigal God and The Reason for God. Collin Hansen (MDiv, Trinity Evangelical Divinity School) serves as the editorial director for the Gospel Coalition. He previously worked as an associate editor for Christianity Today magazine and coedits the Cultural Renewal series with Tim Keller. He and his wife belong to Redeemer Community Church in Birmingham, Alabama, and he serves on the advisory board of Beeson Divinity School. You can follow him on Twitter at @collinhansen. TIMOTHY KELLER is founder and pastor of Redeemer Presbyterian Church in New York. He is the best-selling author of The Prodigal God and The Reason for God.