It is a spiritual realm established in the hearts and lives of believers. He administers His kingdom by spiritual means— the word and the Spirit.
Whenever believers follow the lordship of Christ, the Saviour is exercising His ruling or kingly function. From this, we understand that His kingship is more concerned with Jesus’ reign than with the realm over which this takes place. When we pray “Your kingdom come” as we do in the Lord’s prayer (Matt. 6:10), we have in mind this present rule of Christ the King.
Christ’s kingship is also present today in the natural world. Christ is the One through whom all things came into being (John 1:3) and through whom all things are held together (Col. 1:17). He is in control of the natural universe as He demonstrated during His earthly ministry (Mark 4:35-41).