For if ye forgive men their trespasses, your heavenly Father will also forgive you:  15 But if ye forgive not men their trespasses, neither will your Father forgive your trespasses.

Matthew 6:14-15

If I withhold forgiveness from someone, I create a barrier to my own forgiveness from God.  If I choose to forgive and let God take it from there, healing and restoration comes to me.  When I forgive you, it doesn’t change you, it changes me.  It’s like dropping a stone in a still pond.  It creates a ripple of grace, that gets bigger and bigger and gives God access to change you, too.