Blessed are the merciful, for they will be shown mercy. (Matthew 5:7)
Conversely, if someone can’t be merciful, it’s because they can’t stand living outside the constraints and definitions of the law.
If someone can’t be merciful, it’s because that person can’t stand for someone to get something for free when everybody else has to work for it, even if the person who can’t stand it is the one who gets it for free.
Jesus told the story of a man who, after being forgiven a debt he could not repay, immediately went out and threatened someone who owed him money, but couldn’t repay him. That would be someone who could not, for the life of him, be merciful. He was basically saying he did not want to live in a world where anyone can get something for free (except I notice he didn’t turn down his forgiveness).
Mercy is something you have to give out if you are going to receive it for yourself. You simply can’t have it both ways. You can’t really experience God’s mercy while still wanting everyone else to get what they deserve.
You can see this whole dynamic at work these days in the current debate over immigration laws. America is a country of immigrants. The only ones who truly belong here by right of being here first are Native Americans. Someone like me, of European descent, is here by way of immigration. This is a free country that opened its doors to my ancestors. On what basis do I, then, have the right to close those doors and not let anyone else have what I received freely?
Jesus chided the Pharisees for holding the keys to the kingdom, while standing by the door and refusing to let anyone in. The Pharisees were people who simply could not be merciful. Mercy blew their whole system.
Another parable Jesus told was of the landowner who paid all his workers in the field a full day’s wage, even if they only worked the last hour. The only people this bothered were the people who worked all day. If you work for what you get, then it matters what everyone else gets. If what you get comes by mercy and grace, it matters little (in comparison) what happens to everyone else.
It’s a true test of whether someone belongs to the kingdom of heaven, if Jesus can let in anyone He wants, and it’s fine with them. If there is someone you can’t be merciful to, it’s a pretty good indication you are trying to have salvation by works, and not by grace.