“God’s statement that he desires mercy and not sacrifice is a great passage, in other words, on the importance of social action and meeting physical needs. This is especially clear from the tie with the Parable of the Good Samaritan, where the Samaritan’s actions to meet the man’s physical needs are called “compassion” (Luke 10:33) and “mercy” (Luke 10:37). Jesus also often had compassion on the crowds, resulting in meeting their physical needs (Matthew 14:14; 9:35-36). To be a merciful person necessarily includes being on the lookout to meet physical needs.
But there is something even deeper in Matthew 9:13. When Jesus says “I desire mercy, and not sacrifice” there, he gives it as the reason and foundation for why he is interacting with sinners. For he immediately adds: “For I came not to call the righteous, but sinners.”
At the heart of what Jesus is saying is this: True compassion involves not just taking action to meet people’s needs, but doing this even for the unworthy. “I desire mercy” does not simply mean “do good to those who do good to you.” Jesus is defining true compassion as having love for sinful,unworthy people at its very essence. What the Pharisees didn’t get is that when God calls us to have compassion on people, he doesn’t restrict it to apparently “worthy” people. Love that does not love the unworthy is actually not true love at all. That’s why the call to love one’s enemies is central, not an aside, to the biblical ethic of love (Matthew 5:43-48; Luke 6:27-36; Romans 12:19-21). True compassion has compassion even on sinners, those who have failed, and even one’s enemies.
Which is, of course, all of us (something else the Pharisees didn’t get).
This is why Jesus came to earth. He came because he is a loving, compassionate God, which means not simply that he does good for those who do good, but that he also seeks to rescue those who have done evil. That’s the true meaning of love. That’s Jesus’ point here. “Those who are well have no need of a physician, but those who are sick. Go and learn what this means, ‘I desire mercy, and not sacrifice.’ For I came to call not the righteous, but sinners” (Matthew 9:12-13).
This is also the meaning of John 3:16. “For God loved the world in this way: He gave his only begotten Son that whoever believes in him should not perish, but have eternal life.” That is, God’s love is the kind of love that gives utterly sacrificially even for the welfare of sinners–those who, as John puts it here, are in danger of perishing.
Seeking the welfare of unworthy — demonstrated in action — is part of the very definition of God’s love.
This is why social action is not enough. Love for others will and must manifest itself in meeting people’s concrete, tangible needs for food, shelter, companionship, and purpose in life. But beyond all of these things, we have a more fundamental, even deeper need: we are estranged from God because of our sin. True compassion does not stop at meeting people’s physical and social needs, therefore. It goes all the way and seeks to meet their spiritual need for reconciliation with God as well.”