[The radical commands of Romans 12:14-21] are rooted in Christ-preoccupation and Christ-infatuation and Christ-exaltation . . . The alternative to thinking too highly of ourselves (self-preoccupation, self-infatuation, self-exaltation - the roots of all sin) is not a different sight in the “mirror, mirror on the wall.” The alternative is turn the mirror into a window through which we see the glory of Christ.
That’s what faith is and does. When faith stands in front of a mirror, the mirror becomes a window and sees on the other side the glory of Christ. The decisive alternative to saying, “I am all,” is not to say, “I am nothing,” but to say, “Christ is all.” Faith looks to Christ, not self, not even the new self. In fact the definition of the new-self is the self that looks to Christ as its Savior and Lord and Treasure and Joy and Satisfaction.
John Piper, "Bless Those Who Persecute You," Romans 12:14-21, February 6, 2005.