"Put another way, it is the cross—and the cross alone—which is the gateway to the blessings of the kingdom. That’s how you put all this together. You don’t get the blessings of the kingdom unless you come into them through the blood of the King. Therefore if you preach a sermon or write a chapter on the good news of the kingdom, but neglect to talk about the cross, you’ve not preached good news at all. You’ve just shown people a wonderful thing that they have no right to be a part of because they are sinners. That’s why we never see Jesus preaching, “The kingdom of God has come!” No, it’s always, “The kingdom of God has come! Therefore repent and believe!” He didn’t just preach the coming of the kingdom. He preached the coming of the kingdom and the way people could enter it."
Greg Gilbert, What is The Gospel, quoted at Justin Taylor and Already Not Yet