What does it mean that the kingdom of God is not of this world?

Jesus proclaimed that the kingdom of God is not of this world, as stated in John 18:36. This means that it does not conform to earthly political systems or cultural constructs but instead exists in a spiritual domain where Christ reigns over the hearts of believers. In Romans 14:17, Paul adds that the kingdom of God is characterized by righteousness, peace, and joy in the Holy Spirit. This emphasizes that true fulfillment in God's kingdom comes from His sovereign work within us rather than from external circumstances or worldly achievements.