For he is the 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 the minister of God, a revenger to execute wrath upon him that doeth evil. For he is the minister of God to thee for good - Here the apostle puts the character of the ruler in the strongest possible light. He is the minister of God - the office is by Divine appointment: the man who is worthy of the office will act in conformity to the will of God: and as the eyes of the Lord are over the righteous, and his ears open to their cry, consequently the ruler will be the minister of God to them for good.
He beareth not the sword in vain - His power is delegated to him for the defense and encouragement of the good, and the punishment of the wicked; and he has authority to punish capitally, when the law so requires: this the term sword leads us to infer.
For he is the minister of God, a revenger - Θεοῦ διακονος εστιν εκδικος, For he is God's vindictive minister, to execute wrath; εις οργην, to inflict punishment upon the transgressors of the law; and this according to the statutes of that law; for God's civil ministers are never allowed to pronounce or inflict punishment according to their own minds or feeling, but according to the express declarations of the law.