Basileia tou theou (Greek) or Regnum Dei (Latin) means “Kingdom of God,” and it is a consistent theme. The phrase “the Kingdom of God” is used at least fifty times by Jesus in the Gospels, and it appears almost a hundred times in the entire New Testament. It must be an important idea to be mentioned so often.
When Jesus says that “the Kingdom of God is at hand” in Mark 1:15, He is not speaking of an earthly kingdom or of a territory or place as we know it. Rather than being limited to a geographical location, the Kingdom of God is wherever the Reign of God exists. Wherever men and women accept the dominion of God, that is, allow Christ to reign in their hearts and allow themselves to be governed by God’s will rather than by their own, then the Kingdom of God is present.
An analogy to this would be the Roman Empire if we describe it not in territorial terms but in terms of Roman Law, Roman culture, Roman roads, Roman language (Latin), Roman currency, etc., throughout the Empire. Territorial boundaries are artificial delineations. Likewise, the Kingdom of God is not limited to heaven but is anywhere and everywhere the Reign of God is embraced. Hell is one place where no one accepts the dominion of God.
The Kingdom of God is in our hearts, our minds, and our souls. At the time Jesus walked this earth two millennia ago, people were expecting an earthly or political Messiah who would restore the regal might of Jerusalem and the Kingdom of Israel to something resembling the days of King David and King Solomon. Christ did not come to establish an earthly kingdom but a spiritual kingdom.
The phrase “thy kingdom come” in the Lord’s Prayer refers to the two comings of Christ. Historically, Jesus came two thousand years ago and established His kingdom in the hearts of all the baptized. Eschatologically, (a fancy theological word meaning “at the end of time”), there will be the Second Coming of Christ. At that time, the Devil and those who choose his reign will be cast from this earth into hell, never to escape. The righteous, who have chosen the reign of God, will be with Him forever. The prayer reminds us that there is an end of the world; there is Judgment Day and a Day of Reckoning. The rulers of this world will find out who is really in charge.