Matthew 12:35 A good man out of the good treasure of the heart bringeth forth good things: and an evil man out of the evil treasure bringeth forth evil things.
I think that it is amazing to consider this truth. What we say and do comes out of our heart. We tend to think in terms of externals but God speaks of internals.
The hatred, bitterness, division, etc comes from our hearts. Our unwillingness to forgive, our rebellion, our sin all come from our heart. The real work of the Christian is to work on his heart.
God can change our hearts. We can let go of things. We can overcome. We can have victory.
Change what you are thinking about. Fill up your heart and mind with the Word of God. Get His attitudes from Scripture into your heart.
We will need to work on our hearts and what is happening there more than any other thing!