rejection

What a loving God we serve who forgives us when we wrong Him. So many times the Israelites turn away from God and serve other gods (Judges 10). Yet He has comes to their rescue time and time again. I'm so quick to hold grudges when someone wrong's me or when someone rejects me. I always hope for the worst for someone who does. Or in bad cases actually try and do things to get even or make them feel bad. Why is this? Is it because I feel I'm such a good person and don't deserve bad things should happen to me? I dunno. But it does center around the fact that my mindset is so focused on me. How do I begin to change?