The believer has been placed in a radically new estate in Jesus.  The old things have passed away, and all things have become fresh forever.  This new life that the believer has been given is the very life of God himself.  The old man of the old "life" was done away through our co-crucifixion with Jesus.  We are therefore enjoined to "put" on the new man that was created in the image of him who created him.