Romans 6:5-6

For if we have become one with Him (permanently united) in the likeness of His death, we will also certainly be (one with Him and share fully) in the likeness of His resurrection. We know that our old self (our human nature without the Holy Spirit) was nailed to the cross with Him, so that our body of sin might be done away with, so that we would no longer be slaves to sin.

We change when we are saved. We are no longer the old person unable to make choices that miss the mark of goodness. The selfish old nature perishes, and the new nature of Jesus and love enters our hearts. God can heal our hearts from pain and move us to forgiveness, just as we were forgiven.