Believers in Christ are ambassadors for Christ (2 Cor 5:20), which means we represent Christ’s kingdom on earth. An ambassador is someone that lives in one country but represents another. When we were born again we were made citizens of the new kingdom, we are only here on earth as ambassadors for that kingdom. This means nationalism, has no place in Christianity because the USA, China, and Russia will be destroyed on Judgment Day, and only God’s people will be saved because they are citizens of the Kingdom of Heaven, and as for now they simply are foreigners on earth that work for the heavenly embassy.
This is because believers are in the world but not of the world (John 17:13-19), and are actually citizens of heaven (Phil 3:20-21). When we are “born again”, we get birthright citizenship in heaven because we are now classified as children of God (John 1:10-13, 1 John 3:9-10, Rom 8:7-17). God is a spirit and therefore his children are only those born again in spirit and receive eternal life (John 3:1-15). In the new covenant, the earth is not the home of believers, their true home is the world to come (Heb13:10-14).