Romans 13:5

‘For which reason you must necessarily be in subjection, not only because of the wrath, but also for conscience' sake.'

And it is because the appointed ruler is a minister of God for good that obedience to the requirements of the state, where it does not affect our loyalty to God, is to be seen as necessary. It is a duty not just a convenience. Indeed as Christians our loyalty to the state is for three reasons, firstly because it is an instrument of God for good, secondly because it is the instrument for ‘the wrath' (of God) against evil, and thirdly because Christians should respond positively towards one who is ‘a servant of God', for conscience' sake.

To be in subjection is to respond to legitimate requirements. It does not indicate subservience. The point is that, acting as God's servant the state authority has a right to make certain demands, and unless they go against the conscience they should be obeyed. Compare Titus 3:1.