“Now may the God of peace Himself sanctify you completely; and may your whole spirit, soul, and body be preserved blameless at the coming of our Lord Jesus Christ. He who calls you is faithful, who also will do it” (1 Thess. 5:23,24).
Paul’s prayer for personal holiness for believers in 1 Thessalonians 5:23,24 focuses on your three dimensions: spirit, soul, and body. The passage also contains a petition, a prospect, and a promise.
1. The Petition
Note the petition’s subject: “Now may the God of peace Himself sanctify you completely.” Although he is not referring to sinless perfection in this life or the eradication of the sin principle as an evil influence, Paul looks to God to bring about a holy standard of character and conduct in His children. This is God’s will, for He has said, “Be holy for I am holy” (1 Pet. 1:16).
We were positionally sanctified at conversion (1 Cor. 1:2; 6:11), and we need to live according to this new standing and identity progressively (2 Cor. 7:1). Growth in holiness involves living in harmony with Christ in us, who has already made us partaker’s of His nature (2 Pet. 1;4).
Note also the scope of the petition: “your whole spirit, soul, and body” (v. 23). The human spirit of the believer was made alive at regeneration (Eph. 2:1) and is the dwelling place of the Holy Spirit (1 Cor. 3:16). The believer is now a “new man” as identified by his regenerated spirit: “… the new man which was created according to God, in true righteousness and holiness” (Eph. 4:24). This petition is answered as we allow “the new man” to take dominion over our soul (will, mind, and emotions), and body (1 Cor. 9:27).
Oswald Chambers describes this growth in holiness:
“Sanctification is an instantaneous, continuous work of grace; how long the approach to it takes depends upon ourselves, and that leads some to say that sanctification is not instantaneous. The reason some do not enter in is they have never allowed their minds to realize what sanctification means … It will cost an intense narrowing of our interests on earth, and an immense broadening of our interest in God. In other words, sanctification means an intense concentration on God’s point of view–every power of spirit, soul, and body chained and kept for God’s purpose only.” 
2. The Prospect
The text also has a hope-filled prospect: “your whole spirit, soul, and body be preserved blameless at the coming of our Lord Jesus Christ.” (v.23). How reassuring that God will complete this quest for holiness in the lives of His people!
“Behold what manner of love the Father has bestowed on us, that we should be called children of God! Therefore the world does not know us, because it did not know Him. Beloved, now we are children of God; and it has not yet been revealed what we shall be, but we know that when He is revealed, we shall be like Him, for we shall see Him as He is. And everyone who has this hope in Him purifies himself, just as He is pure” (1 John 3:1-3).
3. The Promise
Then the prayer concludes with a promise: “He who calls you is faithful, who also will do it” (v. 24). This reminds us that it is “the God of Peace” who is petitioned to fulfill this gracious work in our lives. Chambers goes on to affirm,
“If we are to be sanctified, it must be by the God of Peace Himself. The power that makes the life of the saint does not come from our efforts at all; it comes from the heart of the God of Peace. Some use the phrase ‘to pray through’. What we have to ‘pray through’ is all our petulant struggling after sanctification, all the inveterate suspicion in our hearts that God cannot sanctify us. When we are rid of all that and are right before God, then God lets us see how He alone does the work.
When our feeble efforts,
And from struggling cease,
Brings us God’s own peace.” 
May God fulfill the ongoing process of “three-D sanctification” in your life and mine–holiness in spirit, soul, and body–for our health and His honor.
Our Father, we thank You for the prospect of continued growth in practical holiness. We depend upon You, the God of Peace, to set us apart–spirit, soul, and body–for Your wise, eternal purposes. We rejoice that You will accomplish this glorious promise! In Christ’s name, amen.
 See 1 John 1:8; James 3:2/ Gal 5:17
 Oswald Chambers, If Ye Shall Ask, p. 74. Chambers teaches the three part design of man also in his book Biblical Psychology.
 Chambers, p. 77.
Grace Notes (c) 1998, John Woodward. 3nd edition, 2013. Permission is granted to reprint this article for non-commercial use. Scripture quotations are from The Holy Bible, New King James Version (c) 1982 by Thomas Nelson, Inc.
This theme is further explored in the book, Man as Spirit, Soul and Body: A Study of Biblical Psychology (https://gracenotebook.com/man-as-spirit-soul-and-body-chapter-7/).