Be kind and compassionate to one another, forgiving each other, just as in Christ God forgave you.Here is what you are to "put on" in the process of change. You were to "put off" all "bitterness, rage and anger, brawling and slander, along with every form of malice" as described in verse 32, and you are to "put on" kindness, compassion, and forgiveness.
We also get a "mind-renewing" boost at the end of the verse, "just as in Christ God forgave you." When you consider how much you have been forgiven, how much compassion Christ has shown to you, and how much kindness you are shown every day by an almighty God, it becomes more clear why you should show these things to others.
Remember, if you are a child of God, then the process of change is ultimately a work of Christ. Consider Philippians 1:6,
being confident of this, that he who began a good work in you will carry it on to completion until the day of Christ Jesus.Also consider Ephesians 2:10,
For we are God's workmanship, created in Christ Jesus to do good works, which God prepared in advance for us to do.We are a work of God's and He is working all things in our life for the purpose of making us like Christ. Consider Romans 8:28-31
And we know that in all things God works for the good of those who love him, who have been called according to his purpose. For those God foreknew he also predestined to be conformed to the likeness of his Son, that he might be the firstborn among many brothers. And those he predestined, he also called; those he called, he also justified; those he justified, he also glorified. What, then, shall we say in response to this? If God is for us, who can be against us?I included verse 31 because that is the ultimate response that we should have when dealing with sin in our lives. That verse gets misused so often. As you go through this day and God is changing you, just remember that He will succeed.