God punishes Cain for what he's done, but he also disallows anyone else from taking revenge on Cain. The mark of Cain is a call for others to forgive Cain rather than perpetuate the cycle of sin he created. God always interrupts sin with grace and forgiveness.
cycle of sin is God wanting to interrupt in your life? Who has hurt you?
Who do you need to forgive? Imagine them having the mark of Cain not as
a sign of their sin, but as God's call for you to forgive them.