Paul said, "I have been crucified with Christ . . . ." He did not say, "I have made a determination to imitate Jesus Christ," or, "I will really make an effort to follow Him"-but-"I have been identified with Him in His death." Once I reach this moral decision and act on it, all that Christ accomplished for me on the Cross is accomplished in me. My unrestrained commitment of myself to God gives the Holy Spirit the opportunity to grant to me the holiness of Jesus Christ.
He continues through the verse. Go read the whole thing, it is short, but excellent.