One of the first times we see mention of the Gospel of the Kingdom is in Isaiah. Isaiah talks about a messenger running toward the destroyed city of Jerusalem proclaiming the good news that their God is still King. The messenger says that God himself would one day return to the city to set up his Kingdom and bring peace to the land.
Jesus was given a crown of thorns and a robe, and he was lifted up onto a cross rather than a throne. People witnessing his crucifixion mocked him saying, "behold, the king of the Jews!"
But in death, Jesus went from the messenger bringing the good news of God's Kingdom to the King who would reign over it. He defeated sin and evil, and he established a way by which all of his followers could take part in the Kingdom of God.
Today, the Gospel of Jesus, the good news of God's Kingdom, is ours to deliver. Like the messenger that Isaiah foretold, we too are now charged with going out and proclaiming the good news of Jesus to the world.