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.

He's God's helper for your good. But if you do bad, be careful; he has the power to punish, because he's God's representative enforcing justice on those who do wrong.

King James Version

Simple English

* Work in progress - there may be occasional inaccuracies