Blessed are the merciful, for they will be shown mercy. (Matthew 5:7)
While we tend to be more comfortable excusing or condemning specific actions in our lives, Jesus directs His beatitudes at the condition and orientation of our hearts. In this way He sidesteps all our excuses and justifications and cuts to the core of our struggle with sin. "Am I a merciful person?" Jesus forces me to ask this question not of each action individually but of my general character as revealed by the sum of my actions and attitudes.
Mercy looks with compassion on the needs of others, while judgment questions what the poor souls have done to bring this need upon themselves. In this way judgment most often cuts off any hope for a better tomorrow. It is mercy alone that gives second chances. Mercy observes the need and simply helps. It doesn't question their worthiness to receive the help. For example, a merciful person might well question which way is the best way to help the homeless but she will never generalize that many homeless people are in that condition because of their own choices and choose to turn a blind eye to them all.
Mercy also looks with compassion on the sins of others, even when their sin has cost you personally. Again we find that mercy is unconcerned with desert, for forgiveness and mercy are by definition undeserved. When mercy is deserved it is simply justice. Only when it is undeserved can it be called mercy. As Christians we have received mercy from God and therefore ought to dole out mercy in our dealings with others. We must never forget our ongoing need for mercy and that God promises to give mercy to those who are merciful. So we who were reconciled to God by His initiative while as yet we were still His enemies, when we find ourselves in an unavoidable conflict with someone else, have no right to be anything but conciliatory in tone (Romans 5:8-11). We should never be hostile if it can be avoided in any way, but should always seek to be peacemakers as much as it is in our ability (Matthew 5:9).