John 18:36

Jesus explained that He was indeed a king, as He claimed. However, His kingdom was not the type of kingdom that would compete with Pilate’s kingdom by waging war. Jesus was not denying that His kingdom was an earthly kingdom. He was not saying it was only the spiritual rule of God over the hearts of His people. He was not saying that His kingdom had nothing to do with this world either. [Note: Beasley-Murray, p. 331.] This should be clear from Jesus’ other references to His kingdom as being an earthly kingdom. His point was that He and His kingdom were not a present threat to Rome (cf. 18:10-11). The reason was that God had postponed the messianic kingdom due to Israel’s unbelief, though Jesus did not explain this to Pilate.

Jesus’ kingdom is "not of this realm" or "from another place" (Gr. ouk enteuthen, lit. not from this place) in another sense. It will come down from heaven to the earth rather than originating from the earth. It will begin when Jesus comes down from heaven to earth at His second coming.