For our citizenship is in heaven, from which we also eagerly wait for the Savior, the Lord Jesus Christ.
Christians are not only citizens of their nations in this age. They also have a higher citizenship and allegiance to the Kingdom of God. The headquarters of the Kingdom of God is in heaven, where Christ is currently waiting for His time to return and restore the Kingdom of God to this earth.
When Christ returns, Christians will assist Him in spreading His Kingdom around the earth.