Mercy is both not receiving the justice we are due and extending gifts to the poor and those in need. Both find their root in a compassionate heart; a heart that says 'you do not deserve this but you need it'.
It is the cry of the blind man, the sinner in the temple, the father whose son was having seizures, the Canaanite mother whose daughter was imprisoned by demons, and the 10 lepers. Lord, I do not deserve your healing hand but I desperately need it. I have no hope apart from you.
It is the act of loving others as ourselves demonstrated by the Good Samaritan. It is what God desires from us more than sacrifice. It is having a large heart. It is the opposite of a heart of greed. It is a response of a heart that knows I have nothing apart from God's mercy and generously extending a hand toward those in need.
Jesus gives a parable in Matthew 18 about forgiveness. The kicker is that to the extent of the mercy we give is the extent of mercy we will receive.. (See also James 2:13 among others.) It would be easy for me (and is) to gloss over this and think, "Hey I am covered... saved by grace". I tend to interrupt passages like these and Matthew 25 in light of promises we have of our salvation. And I guess that's good so I don't veer toward thinking I can gain acceptance by what I do. But the assurance causes me to blow off the need, the command to extend mercy. I want it for myself but rarely offer it to others. I am quick to judge and slow to extend mercy.
I recall a few years back I heard a sermon on mercy. It was at a time when I was weighing out whether to send this guy on a summer project or not. On paper, he had done some things recently in his life that disqualified him. But I sensed God was telling me to offer him mercy. I called him up and said, "I shouldn't be sending you, but I am gonna give you mercy." I didn't blow off what he did what offered him the gospel. After that summer, he told me he thought of that every day - when he extended the gospel to others, when he faced temptation, when he might have judged others he served with, when he saw people in need . Every day, he thought of mercy. He saw others in the vein of people that just needed mercy and he saw himself as someone who needed mercy.
I wish that story was more common in my life. I wish my first thought was to drop the stone and grant mercy. I wish my first action would be when I see someone in need to get off my donkey and love my neighbor. I wish I was full of the love of God, full of mercy - merciful... like Christ, like the Father.
Lord, I need mercy. May I cry out like the tax collector in temple, "God, have mercy on me a sinner!" May I cry like the blind beggar, "Jesus, Son of David, have mercy on me!" May I be quick to extend mercy to others. Take my greedy heart and make it a heart of mercy.