He promises to give you a new heart.
I will give you a new heart and put a new spirit within you; I will take the heart of stone out of your flesh and give you a heart of flesh (Ezek. 36:26).
God didn't say he would just repair your old, dirty heart. He is going to perorm a complete transplant, taking the old stuborn heart away and giving you a brand new one. Doctors have come to the conclusion that some people's hearts are beyond repair, and the only way for them to survive is for them to recieve a heart transplant. The same is true spiritually; the only way for us to live life the way God wants us to is to get a fresh start. He exchanges the old for the new. When God gives us this transplant, things don;t look the same to us. It's not just  a different attitude, but a brand new life! We don't need to settle for a repair job when God has a whole new, wonderful life for each of us.
see for yourself: Ps. 51:10 Jer. 32:39 Ezek. 11:19 John 3:3