John Wimber in Kingdom Come:
For the first twelve years of my Christian life I gave little thought to the kingdom of God. My pastors and bible teachers had taught us that the kingdom would come at the second coming of Christ and, therefore, had little significance on our lives today….. I find my neglect of the Kingdom remarkable because it is so clearly the center of Jesus teaching… I [now realize] that at the very heart of the gospel lies the Kingdom of God and that power for effective evangelism and discipleship relates directly to our understanding and experiencing the kingdom today.
John Bright in The Kingdom of God:
The gospel according to Mark begins the story of Jesus' ministry with these significant words: "Jesus came into Galilee, preaching the gospel of God, and saying, "The time is fulfilled, and the Kingdom of God is at hand, repent and believe in the gospel" (1:14-15). Mark thus makes it plain that the burden of Jesus' preaching was to announce the Kingdom of God; that was the central thing with which he was concerned. A reading of the teachings of Jesus as they are found in the gospels only serves to bear this statement out. Everywhere the Kingdom of God was on his lips, and it is always a matter of desperate importance.