This is an important (12 minute) video that helps clarify how we read the gospels and talk about the kingdom. I find the reason why Jesus’ Lordship replaces the “kingdom” talk in the epistles to be a very helpful reminder. It is so wrong to pit the “gospel of Paul” and the “gospel of the kingdom against each other!!!
The article Keller refers to is Simon Gathercole, "The Gospel of Paul and the Gospel of the Kingdom" in God's Power to Save: One Gospel for a Complex World? ed. Christopher Green (UK: Apollos/Inter-Varsity Press, 2006).