3 For rulers are not a terror to good works, but to evil. Do you want to be unafraid of the authority? Do what is good, and you will have praise from the same.
The “for” here gives an elaboration on the divine establishment of human government.
rulers are not a terror to good works,
Human governments respect people who keep the law, and their “rulers” show that fact. The state exists so that society is orderly and workable.
but to evil.
Governments will punish law-breakers. The state has the prerogative to punish law-breakers.
Do you want to be unafraid of the authority?
There is no need to fear human government if we respect human laws. There is a proper fear of government when it attempts to keep law and order.
Do what is good,
Doing what is good is obeying human laws.
and you will have praise [commendation] from the same.
Civil government respects and commends those who follow the law.
Allegiance to God does not abrogate our allegiance to the state.
God has delegated the protection of society to the state. The public good is important in God’s economy. Obeying governing brings approval of society.
Paul himself was subject to punishment from governmental authorities, yet he maintained the proper perspective on the role of human government (Ac 16:19-24; 2 Co 11:25). The normal principle is that government is good for society because it provides law and order.
Since government cannot deal with the sin issue, we cannot expect it to reform individuals. Penal punishment does not restore criminals to a better state. Human depravity can be resolved only by a function of God the Holy Spirit. Redemption changes the heart; reformation does not. The state at least can limit the damages of a sinful nature by forcing it to stay within certain legal bounds.
The Biblical Doctrine of the State: http://versebyversecommentary.com/articles/the-biblical-doctrine-of-the-state/