Cain didn’t kill Abel simply because Cain was evil. He killed him because the contrast between Abel’s goodness and Cain’s evil made Cain angry. It made him feel guilty. Abel didn’t have to say anything; Abel’s goodness was a constant reminder to Cain that he was evil. And instead of dealing with his own evil by repentance and change, he got rid of Abel. If you don’t like what you see in the mirror, shoot the mirror.
So what would it be like for any of us to be like Cain? It would mean that anytime some weakness or bad habit in our lives is exposed by contrast to someone else’s goodness, instead of dealing with the weakness or the bad habit, we keep away from those whose lives make us feel defective. We don’t kill them. We avoid them. Or worse, we find ways to criticize them so as to neutralize the part of their lives that was making us feel convicted. We feel like the best way to nullify someone’s good point is to draw attention to his bad point. And so we protect ourselves from whatever good he might be for us…
So the lesson for us is: Everywhere you see some growth, some virtue, some spiritual discipline, some good habit, or good attitude, rejoice in it. Give thanks for it. Compliment it. Don’t resent it. Don’t be like Cain. Respond the opposite from Cain. Be inspired by other people’s goodness.
Love is humble. Love delights in other people’s good. Love doesn’t protect its own flaws. Love takes steps to change them. What a beautiful fellowship where everyone is rejoicing in each other’s strengths, not resenting them! This is what the love of God looks like when the new birth gives it life in the people of God. (John Piper, Finally Alive, pp. 158-159)
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