For he is God’s servant for your good. But if you do wrong, be afraid, for he does not carry the sword in vain. He is God’s servant, an agent of retribution to the wrongdoer.
KJV
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.
ASV
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.