May the God of peace himself sanctify you completely. May your whole spirit, soul, and body be preserved blameless at the coming of our Lord Jesus Christ.
Paul may have mentioned "spirit and soul and body" because these three aspects point to the believer’s relationships to God, himself or herself, and other people. Together they picture wholeness. Paul’s desire for his readers was that every part of them, involving all their relationships, would remain without fault and that they would continue to mature and live free from legitimate grounds for accusation until Christ’s return. Note again that he believed the Lord’s return could precede their deaths.