From Tim Chester’s book, From Creation to New Creation:
It is through the preaching of the gospel that Jesus is wielding His sceptre in the world… Through the gospel we command people to submit to Jesus. Through the gospel judgment is passed on people who continue to reject Him. To tell people the gospel is to announce the kingdom or kingship of God and His Christ.
We are ambassadors for Christ, bringing an authoritative pronouncements from the King. When we preach the gospel, we a re heralds of a coming King. We go to the citizens of a country and say that a King is coming who rightly claims their allegiance. Those who currently rule them are usurpers and tyrants. If they acknowledge His lordship, they will experience His rule as blessing, life and salvation. If they reject Him, they will experience Him as their conqueror and judge.