Growing up unchurched, I often heard religious people talk about the "gospel" but I was clueless as to what they meant. We hear about "gospel singing," "gospel preaching," and the "gospel truth." But if you ask the average person on the street for a definition of gospel, one has no idea how to answer. I'm not convinced that even most religous people know what they're talking about when they say "gospel."
While the term "gospel" is an almost exclusively religous word in our day, the Greek word translated "gospel" in our Bibles did not originally belong to religious vocabulary. The same is true of other terms like "Savior," "Redemption," "Justification" and many others which are now considered high-dollar church words. The biblical authors didn't have any high-dollar church words. They used the existing vocabulary of their culture as metaphors to describe God's plan for reconciling people to himself. Today's theological terms did not start out as exclusively religious currency.
The word translated "gospel" means "good news" or "glad tidings." It was used by the ancients in reference to a new world order. During the reign of Caesar Augustus it was said that the day of his birth was the beginning of the "gospel." Augustus put a stop to the civil wars which followed the assasination of Julius Caesar. The entire known world was united under Augustus as an empire. The coming of this new world order of restored peace was said to be the "gospel" (good news, glad tidings). So Augustus was hailed "Savior of the world." He was called the son of a god, having been adopted by Julius Caesar who was thought to have been deified in death.
So the biblical authors used everyday language to say what was special about Jesus. He preached the gospel of the kingdom, a new world order (Luke 8:1). Hailed as Prince of Peace, Savior of the World, and Son of God, it may have sounded like Jesus was in competition with Augustus and subsequent emperors. Some suspected Jesus' kingdom would be established through a militant revolution. His Jewish followers, unhappy with the Roman occupation of Palestine, were hoping to be led in battle against Rome.
Did Jesus intend to establish a political kingdom brought about by force? On trial before Pilate, accused of insurrection, Jesus said, "My kingdom is not of this world" (John 18:36). Elsewhere Jesus said, "The kingdom does not come with your careful observation...because the kingdom of God is within you" (Luke 17:20-21).
The "gospel of the kingdom" is indeed the "glad tidings of a new world order." The kingdom, however, does not advance by force or political manueverings, but by influence. It is like leaven working through the dough (Matt. 13:33). The subjects of the kingdom are those submitting themselves to the reign of God in their lives. They have believed the good news and thereby make up an alternative community characterized by justice, mercy, and faithfulness (Matt. 23:23).
The kingdom of heaven currently co-exists with other world powers that have sought to bypass God's authority and do things their own way. The wheat and the weeds co-exist, growing together until the return of Christ when they are spearated and his kingdom will be the only one left stadning (Matt. 13:24-43).
In the meantime, believers are to pray for the advancing kingdom. To pray that God's kingdom will come is to pray for it's continued advanement and infleucne in this world (Mat. 6:10). We pray for, and do, God's will on earth, so that more beachheads of the kingdom are established in this world to reflect how things are in heaven where God's rule is unchallenged.