Resentment is, for all practical purposes, emotional masochism. Resentment is emotional masochism. Storing up grievances only brings us shame. In remembering our grievances, we think we're gaining a bit of justice by remembering someone's injustice toward us. But it works exactly opposite in reality.
Resentment is a shameful way of dealing with the past or present.
Ultimately, resentment dares to do what God refuses to do. Remarkably, God reconciles, rather than resents. God was reconciling the world to himself in Christ, not counting men's sins against them. God is love. And for those who claim to know God, reconciliation is the only way to life and love.