"Blessed are the merciful, for they shall receive mercy." (Matthew 5:7) (NRSV)
Most Christian commentators of my acquaintance argue the first four beatitudes deal with the interior life, then go on to say that the fifth beatitude stikes off in a new direction, namely behavior. I think the distinction too neatly drawn. All the beatitudes assume a vital connection among one's heart, mind, tongue, and hands. They deal with the whole person.
The fifth beatitude calls for those who would live under the rule of God to act mercifully toward others. Micah 6:8 no doubt informed the beatitude ("What does the Lord require of you? To do justice, and to love mercy, and to walk humbly with your God.") Various commentators note that late in the first century C.E., Gamaliel II said, "So long as you are merciful, the Merciful is merciful to you." In short, the core concept was in the air.
That's not to say it was the majority position in first century Jewish life, let alone broader Graco-Roman culture. The position's call for mercy naturally raised the question of limits. Should such mercy be extended to the Romans, in other words even to one's oppressors? Did the mercy requirement cross religious and ethnic boundaries (example: the Samaritans)? Could someone's decisions and actions place him or her beyond the possibility of mercy (think of the parable of the Loving Father and His Two Sons)? I think we continue to ask the same questions. Only the examples have changed.
What about justice? If living under the rule of God required that one become merciful, who would ensure justice was done? Rami, a Jewish friend in another part of the USA pointedly raised this question in a group setting. He said (more or less): "You people (he meant Christians) don't get it. We (he meant Jews)aren't interested in grace or mercy toward those who try to kill us. Only justice will suffice. Mercy changes nothing. In fact, it only encourages the oppressors. Justice, though, strikes the needed blow. The world needs justice, not mercy." He was angry, of course. Knowing him, I think his emotion led him to overstate his point. Still, it was well made, and it gave me pause. I suspect this kind of question lurks in the back of the minds of most of us.
Jesus was a visionary. We must keep this in mind as we wrestle with the fifth beatitude. When all live under the rule of God, mercy and justice become one. In the meantime, those who willingly subject themselves to God's rule experience his mercy. As we come to grips with being forgiven by the One who is just beyond our comprehension, our potential for practicing mercy toward others grows. Strangely enough, the more mercy we extend the more aware we become of the mercy we receive, both from God and others.
At the personal level, the practice of mercy changes us. Over time it blunts resentment, reduces our thirst for revenge, expands our friendship circles, teaches us to pause before reacting, induces empathy, and fosters humility.
Lest I sound naive, I hasten to add that mercy-granting is dangerous in the world as it is. The merciful are blessed, but they may also be victimized by the violent, greedy or vengeful. The merciful may find they are prime candidates for martyrdom. Christians, of course, do well to remember a phrase Jesus spoke from his cross: "Father, forgive them, for they do not know what they do."