How did a holistic benediction become a basis for separating a human being into three parts: the spirit from the soul, and the soul from the body? (I Thessalonians 5:23) The Apostle Paul was a Jew, and the Hebrew people never taught that a human being was composed of three distinctive parts. The Hebrew word for “soul” means “living being” (Genesis 2:7).
Joshua 10:28-39 makes this very clear, as do many other Old Testament texts. In the King James Version, Joshua 11:11 reads: “And Joshua smote all the souls that were therein with the edge of the sword.” The New King James Version reads: “And they struck all the people that were in [the city] with the edge of the sword.” Smiting the psychology of people with the sword would be quite difficult. Then there’s “he who wins souls is wise” (Proverbs 11:30). Would he not be wiser to win the spirit and body as well? You’ve probably got my point, but if not a study of the word “soul” will prove helpful.
What then of Hebrews 4:12, which states that only God’s word can separate between “spirit, and soul, and body” – does this verse not prove that a human being is composed of three distinct parts? Not if we are familiar with “Hebraisms”: expressions distinct to the Hebrew language. Here’s another: Loving the LORD “with all your heart, with all your soul, with all your mind, and with all your strength” (Mark 12:30). In a word, entirely!
Then there’s the “good and acceptable and perfect” will of God (Romans 12:3). Not three levels of will but one will that includes all three aspects!
Matthew 28:19 might well be another: “In the name of the Father, and of the Son, and of the Holy Spirit.” We can study the “name” of the Father, and we know that the “name” of the Son is Jesus, but what is the “name” of the Holy Spirit? Might it not be about “name” as such but rather about God’s authority in its entirety? If so, might it explain why it is nowhere recorded that the apostles baptised “in the name of Father, and of the Son, and of the Holy Spirit” but rather “in the name of Jesus” – who has “all authority in both heaven and earth”?
My belief is that First Thessalonians 5:23 is a Hebraism, and as such was not written to differentiate between spirit, soul, and body (which Hebrews 4:12 informs us only God’s word, can do). Paul’s words comprise a doxology: a blessing pronounced not a division made. It is holistic, in that it is inclusive of all that we are as human beings and as Christians.
The literal NT Greek reads: “Now may the God of peace Himself be hallowing you wholly [making you entirely whole]; and may your unimpaired spirit and soul and body be kept blameless in the presence of our Lord Jesus Christ.” Paul pronounces a similar doxology in Second Thessalonians 3:16: “Now may the Lord of peace Himself give you peace continually by every means. The Lord be with you all.”
So, how about getting out of bed in the morning and saying with gusto: “Praise God, I am entirely whole in all that I am — in every part of me! I declare it in the Name of Jesus Christ my Lord!”
If you disagree with the above in a courteous way, that’s fine; it suggests that you are capable of disagreeing without being disagreeable. 
We’re all on a learning curve and will remain so until we see the Lord face to face and know even as we are known.
Meanwhile, let’s remember that we’ll soon live together forever, and with that in mind, practice loving each other in the time we have left.