For rulers are not a terror to the good work, but to the evil. And wouldest thou have no fear of the power? do that which is good, and thou shalt have praise from the same:

4 for he is a minister of God to thee for good. But if thou do that which is evil, be afraid; for he beareth not the sword in vain: for he is a minister of God, an avenger for wrath to him that doeth evil.

(Rom. 13:3-4 ASV)

The duty of the ruler is to reward good, and punish evil.