Therefore you must be subject, not only for wrath, but also for conscience's sake.
Read Chapter 13
Ambrosiaster
AD 400
One must be subject … because of the coming judgment, for whoever escapes now will be punished then, his own conscience accusing him. Commentary on Paul’s Epistles.
This is helpful for understanding that because of this life we must be subject and not offer resistance if anyone wants to take something from us, if it is in his power to do so, because authority has been given to him over temporal things, which will pass away. We are not to be subject in those good things which remain forever but only in the needs of this age. But when he says “one must be subject,” lest anyone submit to the authorities halfheartedly and not from pure love, Paul adds: “not only to avoid … wrath but also for the sake of conscience.” That is to say, you should not submit simply to avoid the authority’s anger, which can be done by pretense, but so that you might be assured in your conscience that you are doing this out of love for him. For you submit at your Lord’s command.
What is the meaning of “not only to avoid God’s wrath”? It means not only because you resist God by not being subject, nor only because you are bringing great evils on yourself both from God and from the ruler, but also because the ruler is a benefactor to you in things of the utmost importance, because he brings you peace and the blessings of civil institutions. States receive countless blessings through these authorities, and if they were taken away, everything would go to pieces.