"He has showed you, O man, what is good. And what does the LORD require of you? To act justly and to love mercy and to walk humbly with your God" (Micah 6:8, NIV).
How can we be people of justice and people of mercy at the same time? John Piper shares some great insights in his sermon, "When Is It Right to Repay Evil with Pain?" It may be read or heard at http://www.desiringgod.org/ResourceLibrary/Sermons/ByDate/2005/206_When_Is_It_Right_to_Repay_Evil_With_Pain/. It is worth reading and considering.