Even as new creations in Christ we are warned to not be conformed to this world but be transformed by the renewing of our minds. We have the Holy Spirit living within us but remain in the flesh until Jesus comes. And the flesh and spirit are in opposition to one another. We are barraged by the world we live in on an ongoing basis. Our flesh is susceptible to the enticements of the world and if we are not secure in who we are in Christ we can find ourselves once again being conformed to this world. 
We were created for eternity and God has placed eternity within each one of us. When we attempt to fill that eternal void in our lives with anything other than God's love and grace we will revert back to the conformity of this world. 
God desires for us to become partakers of His divine nature not to walk in the corruption of the world living by our old destructive lusts. When you and I forget about the love that God has for us we will allow the things of this world to take its place. Transformation is about living in the love relationship of Jesus Christ and experiencing the power of His grace.