Romans 13:1–7 Every person is to be in subjection to the governing authorities. For there is no authority except from God, and those which exist are established by God. Therefore whoever resists authority has opposed the ordinance of God; and they who have opposed will receive condemnation upon themselves. For rulers are not a cause of fear for good behavior, but for evil. Do you want to have no fear of authority? Do what is good and you will have praise from the same; for it is a minister of God to you for good. But if you do what is evil, be afraid; for it does not bear the sword for nothing; for it is a minister of God, an avenger who brings wrath on the one who practices evil. Therefore it is necessary to be in subjection, not only because of wrath, but also for conscience’ sake. For because of this you also pay taxes, for rulers are servants of God, devoting themselves to this very thing. Render to all what is due them: tax to whom tax is due; custom to whom custom; fear to whom fear; honor to whom honor.
Romans 12:17b Respect what is right in the sight of all men.
1 Peter 2:13–14 Submit yourselves for the Lord’s sake to every human institution, whether to a king as the one in authority, or to governors as sent by him for the punishment of evildoers and the praise of those who do right.
At the end of the day, we each have to study the Word for ourselves and come to our own conclusions as to what is right in the sight of God or not. If for you, that means that flying the nation’s flag in church is wrong, then so be it.