For he is the minister of God to you for good. But if you do that which is evil, be afraid; for he bears not the sword in vain: for he is the minister of God, an avenger to execute wrath upon him that does evil.
All Commentaries on Romans 13:4 Go To Romans 13
Ambrosiaster
AD 400
Since God has ordained that there will be a future judgment and he does not want anyone to perish, he has ordained rulers in this world who, by causing people to be afraid of them, act as tutors to mankind, teaching them what to do in order to avoid future punishment. Commentary on Paul’s Epistles.