The Greek word for kingdom, reign, or royal power, appearing 162 times — and the central theme of Jesus' preaching. "The kingdom of God" (hē basileia tou theou) was the heart of Jesus' message: "The kingdom of God has come near. Repent and believe the good news!" (Mark 1:15). It refers not to a geographic territory but to God's active reign — His sovereign rule breaking into the present age.
Jesus spoke of the basileia more than any other topic, using parables to reveal its surprising nature: it starts small like a mustard seed (Mark 4:31), is hidden like leaven (Matthew 13:33), and is worth everything you have (Matthew 13:44–46). The kingdom is both present ("the kingdom of God is in your midst" — Luke 17:21) and future ("your kingdom come" — Matthew 6:10). This "already/not yet" tension defines Christian existence between the first and second comings of Christ.
The basileia of God subverts every human power structure. Its king enters on a donkey, not a war horse. Its power is displayed in a cross, not a throne. Its citizens are the poor in spirit, the meek, and the persecuted (Matthew 5:3–10). The relationship between the "kingdom of God" (Mark/Luke) and the "kingdom of heaven" (Matthew) is debated — most scholars consider them synonymous, with Matthew using "heaven" as a Jewish reverence for the divine name.