Building on what his father taught him, David has developed new paradigms of integrating and applying apologetics with evangelism. Together with his late father, Dr. Norman Geisler, David co-authored the book “Conversational Evangelism,” which has since been translated into six languages. David is currently pioneering a 4 R’s model (Rooted, Rested, Ready, Reaching) that integrates apologetics, evangelism, and discipleship, based in part on what David also learned from his friend and mentor Rev. Edmund Chan.