This episode initially addresses the question based on Christ's interaction with Pilate in John 18:36 and John 19:11. Based on the other worldly nature of His kingdom, Christ told Pilate that his disciples didn't need to fight to protect Him. His kingdom would advance, and worldly "encouragement" or opposition is simply not a factor. Even though Christ acknowledged Pilate's DELEGATED authority in John 19:11, He doesn't make His kingdom "dependent" on Pilate's benevolent or adverse participation. Christ is crucified because He chose to lay His life down, and the kingdom of Christ is not beholden to Pilate, and by extension ANY KINGDOM of this world. The late John McArthur concluded the same, even claiming that "Christian nationalism doesn't exist." The episode concludes with a brief analysis of Matthew 28:18-19, whereby Christians are called to respond to the universal authority of Christ by making disciples from all the nations. Christ's dealings with Pilate and His subsequent instructions in the Great Commission reveal how believers are to interact with nation-states as we make individual disciples for Christ.
Government, its Institution and Purpose
To properly answer a question on Christian nationalism, one needs to know the Biblical reason behind the institution of government along with its purpose. Government was instituted in Genesis 9:6 in response to the astronomical murder rate prior to the flood. Government was called to execute murderers, and Paul would later describe its purpose, "to bring wrath on the one who practices evil." (Romans 13:4) Very critically, the government that Christians were called to submit to was the Roman Empire led by Nero, and all examples of government authority instituted by God in the New Testament are secular. Nevertheless Christians are obliged to submit themselves based on universal apprehension of the moral law. Based on the moral law alone (apart from "Christian" law), secular princes execute justice, which prescribes penalties for breaking the law. Additionally, Christ Himself, facing unjust execution, nevertheless acknowledged Pilate had authority over Him because it was given ultimately by God. (John 19:11) The biblical description of government that emerges is one in which God accomplishes His purposes of restraining evil through secular governments, and this conclusion should inform the answer regarding Christian nationalism.