Transformation

Romans 12:2 ESV

2 Do not be conformed to this world, but be transformed by the renewal of your mind, that by testing you may discern what is the will of God, what is good and acceptable and perfect.

The Greek for conform implies something self fashioned. This implies something of the world, for that is what we are capable of fashioning on our own.  Thinking only in worldly terms might then be likened to idol worship, when something replaces God in our worship and affection. It is a union away from union with God. 

Transformation and renewal only takes place in the presence of God. He is present in the Holy Spirit. We are to be present to Him. 

Paul calls us into the intentional action of doing and being on our part. Union requires participation by both parties. It is the will of both.