Put on then, as God’s chosen ones, holy and beloved, compassionate hearts, kindness, humility, meekness, and patience, bearing with one another and, if one has a complaint against another, forgiving each other; as the Lord has forgiven you, so you also must forgive. And above all these put on love, which binds everything together in perfect harmony.
Colossians 3:12-14

Perfect harmony comes at a high price. Forgivness, patience, compassion, kindness, humility - well, the list is right in these verses. We are to 'put it on', because we are chosen, holy, and beloved. Seems like it would be sufficient motivation. We are to live up to the character which has been imputed upon us by the new birth. Being washed in the blood of Christ, our new nature should reflect Christ. But we still have to 'put it on'.

I liked how John Piper put it...

"A Christian is not a person who experiences no bad desires. A Christian is a person who is at war with those desires by the power of the Spirit. Conflict in your soul is not all bad. Even though we long for the day when our flesh will be utterly defunct and only pure and loving desires will fill our hearts, yet there is something worse than the war within between flesh and Spirit—namely, no war within because the flesh controls the citadel and all the outposts. Praise God for the war within! Serenity in sin is death. The Spirit has landed to do battle with the flesh. So take heart if your soul feels like a battlefield at times. The sign of whether you are indwelt by the Spirit is not that you have no bad desires, but that you are at war with them! "

This battle within should produce amoung the people of God perfect harmony as we submit to the Spirit. Here comes that lovely word again - obedience. If we 'put on' the behaviours that the Spirit manifests in us we are being obedient to the voice of Jesus.

Should we use our willpower to obey? Yes. Mightily. "Work out your salvation with fear and trembling; for it is God who is at work in you, both to will and to work for His good pleasure" (Philippians 2:12-13).