What does the Bible say about the nature of Christ's kingdom?

In Luke 9, Jesus clearly articulates that His kingdom is not of this world, but rather a spiritual realm defined by humility and service. The disciples initially misunderstand this, expecting an earthly reign that elevates them in status. However, true greatness in the kingdom of Christ is measured by how one treats the weak and humble, as symbolized by Jesus taking a child and emphasizing the importance of receiving those who are lowly. This contrasts with worldly notions of power and prestige, underlining that in Christ's kingdom, greatness comes from serving others and reflecting Christ's humility.