In my blog posting Ethics – People Do Not Lose Their Minds, I described man as a unity of two parts, those being body and soul, and l claimed that In the Bible the mind and the soul are the same thing. Accepting this truth that the mind and the soul are one-in-the-same is important to understand the truth that people, even those with dementia, do not actually lose their minds.
Although many theologians agree man is a unity of two part, those being an immaterial body and a material soul, there are contemporary Christians who claim man is made of three parts, those being body, soul and spirit, where the mind is placed with the soul and separated from the Spirit. I would like to provide evidence for my claim that man is a unity of two parts, body and soul, where the mind and the soul are one-in-the-same.
Others have laid out the Bible’s teaching on this topic. Rather than repeat these detailed arguments, I plan to provide a brief outline address why it matters that we get this description of man right.
In describing the two parts of man presented in the Bible, I have chosen to use the word “body” to represents the material part of man and “soul” for the immaterial part. For each of these, the Bible uses a variety of words. God, in His wisdom, inspired many authors, from many generations and in many different contexts, to write, utilizing the various writing styles and personalities of each of these authors to record His word. In spite of the resulting variety in the descriptions of body and soul, God made sure, as he does with all concepts, that these are presented consistently. This means the Bible, if interpreted correctly, cannot mean in one place man is made of only two parts and in another place man is made of three parts. In my essay, Comments on the Doctrine of Body and Soul,  I wrote, “Soul may be denoted by Spirit, soul, mind, heart, inner man, etc. Body may at times be interchanged with the flesh. Also, some words such a spirit and flesh are used differently in the Old and New Testament.” 
A study of the Bible shows man is a unity of material and immaterial components. This is accepted by both those who hold to a two part and those who hold to a three part view of man. Those who hold that man has three parts include a material body, an immaterial spirit, the part that worships God and a soul, where intellect and emotion are found. The soul part by some is included with the immaterial and by others with the material part of man. A careful look at the Bible, as a whole, shows it does not present the immaterial part of man divided up in any consistent way. There are some verses describing man with three terms, body, soul and spirit. There are also verses using four terms like, heart, soul, strength and mind. Does this mean we should say man is made of four parts? The place to start is with God’s description of the creation of man in Genesis 1. God made man from the dust of the ground (the material part) and breathed into man the breath of life, (the immaterial part). No other parts are mentioned. There are numerous other scriptures clearly referring to man as a body and a soul. For a detailed presentation and discussion of biblical passages involved I direct you to the following.
– Adam Clark’s book The Biblical Doctrine of Man, Chapter 7, Dichotomy and Trichotomy
– A 4 part series by Andy Underhile in his blog Contr Mundrum found at https://andycontramundum.blogspot.ca/2011/09/why-trichotomy-is-wrong-biblical.html
– An article by Dr Joseph R. Nally Jr. titled Trichotomy or Dichotomy posted on Reformed Answers found at http://reformedanswers.org/answer.asp/file/40572 (as of Mar 1, 2019, this site has no https)
– An article by Hank Hanegraaff titled Body, Soul, and Spirit: Monism, Dichotomy, or Trichotomy? posted on Christian Research Institute found at https://www.equip.org/perspectives/body-soul-and-spirit-monism-dichotomy-or-trichotomy/
– A four part series on dichotomy, focusing on the biblical mean of soul, spirit, mind, and heart, by Sam Storms. —Part One, —Part Two, —Part Three, —Part Four
Sam describes himself as an Amillennial, Calvinistic, charismatic, credo-baptistic, complementarian, Christian Hedonist
Sam Storms concludes his series asking, “is there no distinction at all among the various terms used to describe the immaterial dimension of who we are?” He concludes,
Yes there is. But the distinction is one of function or expression, not of substance. In other words, the various terms point to a variety of exercises, functions, or activities of any particular person, but not to separate or divisible faculties. Thus we might conclude this way:
The “soul” is the whole immaterial being of a man or woman. When the “soul” engages with God it is frequently spoken of as the “spirit”, but on several occasions the “soul” itself engages, communes with, and worships and loves God. When the “soul” is viewed in its capacity to think and reason it is called the “mind”. When the “soul” functions in its volitional capacity or its power to make choices it is called the “will”. When the “soul” feels or experiences intense passions or longings it is called the “affections” or “emotions” or the more vivid “kidneys” or “bowels of compassion” or the like. And when the “soul” is spoken of comprehensively, inclusive of all the above as the center of our innermost being, it is frequently called the “heart”.
But even then we must remember that all of these functions and terms are by and large interchangeable. The “heart” also thinks and loves and serves, as does the “soul” and the “mind” and the “affections”. We engage with God and experience intimacy and communion with him not only in our “spirit” but also with our “will” and our “emotions”.
It does matter that we understand the makeup of man as a unity of two parts, body and soul. Gordon Clark points out, we need to keep in mind ” Christianity is a system of doctrine.” A change in one doctrine impacts the rest. He points out, this doctrine affects ones understanding of the nature of Christ, how one views the Holy Spirit, and the understanding of regeneration and sanctification.  Much can be written to describe the impact of a three part understanding of man. I will mention a couple of problems and point you other writers for more detail.
The three part view of man tends to lead to a false understanding of Christ. An early three part view of man was developed by Apollinaris in the 4th Century to try to explain the relationship of God to man in Christ. Apollinaris taught that in Christ God took on a human body comprised of a physical body and and animal soul, making Christ a three part being, the parts being God, physical body and an animal soul. This doctrine of Christ was declare a heresy, as it makes Christ not fully human, having only a human body and a human-animal soul. Instead of a human spirit, this Christ has a divine spirit. Andy Underhile points out the blog series he wrote on this topic, that “Christianity has always affirmed that Christ is fully God and fully man – two natures, not intermingled – by a mystery of divine wisdom united in One Person, in such a way that Christ is one person with two natures (His human nature and His divine nature). Christ is not a human person [soul] and a Divine Person [Spirit] sharing a body.” Appollinaris’ Christ being not fully human, is not, in human nature, just like us, yet without sin. As such this Christ to rightly die in our place.
Another issue is that the three part view of man robs us of the comfort afforded to Christians who equate the mind with the eternal soul and understand it is not lost or destroyed, as it appears it is, in dementia. (Remember in the two part understanding of man the soul and the mind represent the same thing.) The thee part view makes the spirit eternal and the body of mortal dust. But what about the soul in the body-soul-spirit man? Since it would not be spiritual like the spirit, we could be tempted to view this soul as part of mortal man, the part formed from the dust of the earth, inhabiting the brain, maybe even the brain itself. Actually, one adherent of the three part view does just this. He describes the spirit as the part that worships and eternal. He describes the soul as containing the conscious and unconscious minds, the emotions and the will, and, interestingly, places the soul as part of the earthly, calling the soul “a different kind of materiality.” [*5*} When this bodily function is lost, such as when brain function is lost then such a soul can be lost too. As, I consider this, I also wonder if the resurgence of the three part view of man in our day, is partly responsible for many churched people accepting the idea of organ donation from the, so called, brain dead.
For more on the problems arising from holding to a three part view of man I direct you to the following,
-parts 3a and 3b of the 4 part series Andy Underhile in his blog Contr Mundrum found at https://andycontramundum.blogspot.ca/2011/09/why-trichotomy-is-wrong-3-the-errors-it.html and at httsp://andycontramundum.blogspot.ca/2011/09/why-trichotomy-is-wrong-3-b-errors-it.html
– Brian Onken’s posting titled DANGERS OF THE “TRINITY” IN MAN found at https://www.xtianity.com/tfc/Trinity%20in%20Man.htm
– a essay by Matthew Brown titled Trichotamists, Charismatics and 1 Corinthians 14 found at https://www.the-highway.com/tricho-charis_Brown.html
I hope I have said enough to encourage you to embrace the two part view of man. If not embrace, to wonder about it enough to look at the material I referred to and study the scriptures on this issue.
 Another difference is that flesh in the Old Testament refers more to the body (Gen 2:21, 6:3,13, 9:4,17:14, Lev 13:2, Jug 8:7, 1Sam 17:44, etc) whereas in the New Testament it often refers to man’s sinful nature (Rom 3:20, 6:19, 7:15,25, 8:4) which we think of as part of man’s soul. Gordon Clark writes,
Through both Testaments regularly use popular imprecise language, the New differs from the Old by introducing something more technical. The Aprochrypha and Philo used the terms soul and spirit with greater attention to psychological niceties. Their phraseology filtered down intgo the common speech. The New Testament uses these terms, then, in a way somewhat different from the parallelism of the Psalms, while also reflecting the older usage. The difference in usage is more clear and consistent with the adjectives soulish and spiritual, than the nouns. In James 3:15 there is a wisdom that is “earthly, soulish, demonic” Jude 19 speaks of men who are soulish and not having a spirit…
 Adam Clark, The Biblical Doctrine of Man, p. 44.
 In my posting above, I paraphrased this quote to avoid a theological words not often used. The quote word-for-word is.
Orthodox Christianity has always affirmed the Hypostatic Union of Christ. This means that Christ is fully God and fully man – two distinct natures, not intermingled – by a mystery of divine wisdom hypostatically united in One Person. Christ is not a human person and a Divine Person sharing a body.