Your question contains a small irony. Each component in your quartet (viz., soul, spirit, and heart) is invisible, and you are asking for a diagrammatic representation! (My observation is just an aside.)
If, however, I were to diagram your three highly abstract words, I'd probably draw a heart; you know, the typical Valentine's Day heart, which is probably recognized universally (at least in literate cultures) as a symbol for heart. I'd then draw a straight line down the middle of the heart, from the indented part at the top, to the rounded part, below. I'll explain the diagram later in my answer.
Let's start with the word heart. The word heart, of course, can be defined both literally and figuratively, with a good deal of overlap between the two, since with virtually all metaphors, separating the figurative from the literal is very tricky indeed! Allow me to ensconce the word heart in a sentence, which I'll use as a springboard for this section of my answer. If I am correct, the word, as ensconced, will have, potentially, great heuristic value.
"I can just tell that Jim's heart isn't in the project."
So let's say Jim works in the R & D Department of the ACME Mousetrap Company. His department has been charged with "building a better mousetrap," and Jim is heading up the project. Jim has an assistant working with him as liaison between him and all the department heads within the company. The above quotation came from Jim's assistant.
How and why, do you think, Jim's assistant arrived at the conclusion which I've summarized in the words, "I can just tell that Jim's heart isn't in the project"?
If you suggest that the assistant says that Jim
- complains to his assistant how stupid he thinks the project is,
- fails to meet the various deadlines associated with each stage in the project,
- starts delegating too much responsibility to his assistant,
- comes in late to work, takes extra-long lunch breaks, and
- is in the process of revising his resume,
then you'd be spot on regarding the why of my question. The assistant is saying:
"Jim shows a lack of enthusiasm for the project. Period."
In other words, when someone does not put his or heart into a project, he or she will evince a lack of enthusiasm in attitude. Nonverbal clues alone will clue everyone in that Jim is not a happy camper!
In summary up to this point, then, HEART is revealed in at least some of the following:
Put differently, your heart involves your entire person--intellect, emotion, and will (or spirit, soul, and body).
A song I heard when I was a kid had a simple title: "Heart," by Van Buren. It's from the Broadway musical, "Damn Yankees!" Its lyrics are as follows:
HEART (by Van Buren)
You've gotta have heart
All you really need is heart
When the odds are sayin' you'll never win
That's when the grin should start
You've gotta have hope
Mustn't sit around and mope
Nothin's half as bad as it may appear
Wait'll next year and hope
When your luck is battin' zero
Get your chin up off the floor
Mister you can be a hero
You can open any door, there's nothin' to it but to do it
You've gotta have heart
Miles 'n miles n' miles of heart
Oh, it's fine to be a genius of course
But keep that old horse
Before the cart
First you've gotta have heart
The apostle Paul referred to the heart in the following way:
"and hope does not disappoint, because the love of God has been poured out within our hearts through the Holy Spirit who was given to us (Romans 5:5 NAS).
No wonder the world (in the Johannine sense, as in 1 John chapter 2) links the romantic aspect of heart with the word love! And rightly it should, minus the worldly aspects of course!
The Scripture, on the other hand, while not unaware of the importance and significance of romantic matters of the heart, emphasizes the function of the heart as the seat of emotions, generally. Paul admonishes us in his letter to the Colossian Christians,
"Set your affection on things above, not on things on the earth" (Colossians 3:2 KJV).
Again, to set one's affection on "things above" requires a commitment of the entire person: intellect, emotion, and will.
Spirit can frequently substitute for heart, as in
"I can just tell that Jim is dis-spirited about having to head up the project."
In biblical terms, however, when we think of spirit, we need to think of the God-awareness in each of us, particularly Christians.
Upon being born again, the Christian's spirit became united and indissolubly linked to God's Spirit in an eternal bond. This linkage or union does not automatically result in God-focused, God-honoring, God-pleasing behavior on our part, however. Otherwise, Paul would not have had to say to the Romans,
"For the mind set on the flesh is death, but the mind set on the Spirit is life and peace, because the mind set on the flesh is hostile toward God; for it does not subject itself to the law of God, for it is not even able to do so, and those who are in the flesh cannot please God. However, you are not in the flesh but in the Spirit . . ." (8:6-9a NASB).
I suggest that in these verses Paul equates spirit with mind, even though he does not use the word spirit with a lowercase S. Christians relate to the Spirit--with an uppercase S--with our spirit--with a lowercase S. Furthermore, mind and spirit are two words which frequently denote the same thing; namely, the symbol-mediated (i.e., language-mediated) thought process which fills virtually every waking (and perhaps sleeping) moment of our lives.
That process can be both inner-directed and outer-directed, as we relate to ourselves intra-personally, and to others interpersonally, whether in the silence of our word-mediated thoughts or in verbal and/or nonverbal (including sign language) exchanges with others. When that thought process is directed heavenward, as it were, and toward God, we engage our spirits in communication with the Almighty, through our Lord and Savior, Jesus Christ.
Helping that process "stay on track," so to speak, is God's word, which is living and active in our lives,
". . . sharper than any two-edged sword, and piercing as far as the division of soul and spirit, of both joints and marrow, and able to judge the thoughts and intentions of the heart" (Hebrews 4:12 NASB, my emphasis).
Interestingly, the writer to the Hebrews tells us God's word targets the division between soul and spirit. Why?
I suggest that soul is that part of the inward process I described above which starts as primarily self-directed and self-motivated thought or ideation, and then is externalized and primarily conscious behavior: I think, therefore I am, therefore I act.
God needs to separate soul from spirit in us because our soul is by nature--the "old nature," that is--self-centered and selfish. True, there is no way for us not to be self-centered in the sense that it is not possible to cease beings ourselves and start living as someone else. Even if we could, we would still be living a self-centered life, but as that other person. As the preacher once said, God doesn't create duplicates, only originals. Even as we begin to grasp the meaning of Paul's words in Galatians 2:20,
"I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave himself for me,"
we realize Christ does not desire to take over our identity, personality, and temperament; rather, he wants these things to take on the character of Jesus, and to do so in His strength, not ours.
So the Bible condemns a selfish life and selfish behavior. It labels them as "the flesh" (not "the flesh" as Paul used it in Galatians 2:20, above, where he means "my body"). The Bible enumerates the "works of the flesh" in Galatians chapter 5:
"Now the works of the flesh are evident, which are: adultery, fornication, uncleanness, lewdness, idolatry, sorcery, hatred, contentions, jealousies, outbursts of wrath, selfish ambitions, dissensions, heresies, envy, murders, drunkenness, revelries, and the like; of which I tell you beforehand, just as I also told you in time past, that those who practice such things will not inherit the kingdom of God" (vv.19-21).
Jesus gave us a similar list in Matthew chapter 15 and Mark 7, which I've conflated as follows:
"'But the things that proceed out of the mouth come from the heart, and those defile the man. For out of the heart come evil thoughts, sexual immorality, murders, adultery, greed, theft, malice, false testimony, slander, lewdness, envy, deceit, arrogance, and folly'" (v.19 and vv.21-22, respectively, NIV).
Neither Jesus nor anyone else in the Scripture condemned the human body as being somehow evil. Obviously, the body can be a vehicle for "flesh," but it need not be. Just as a married couple can use their bodies within the marriage covenant to give one another sexual pleasure, so also can that same couple experience sexual pleasure in adulterous affairs. The former use is sanctioned and encouraged by God; the latter is proscribed and condemned. Hebrews tells us,
"Marriage is to be held in honor among all, and the marriage bed is to be undefiled; for fornicators and adulterers God will judge" (13:4 NAS).
Come up with the "opposites" of each item in the lists I've quoted above, and you'll get an idea of how God wants us to think and behave in God-honoring ways. Using only Jesus' list in this way, we can turn
evil thoughts into thoughts about what is true, honest, just, pure, lovely, of a good report, virtuous, and praiseworthy (Philippians 4:8 KJV)
sexual immorality, adultery, and lewdness are into sexual morality, fidelity, purity, and modesty
murderous thoughts and actions into life-giving, life-honoring, life nurturing, and life-empowering thoughts and actions
envy into generosity
deceit and false testimony into honesty
slander into only "good reports" and edifying comments to and about other people
arrogance into humility, and
folly into wisdom
By doing all the above (and the list is only partial), as the Spirit takes God's word and applies it to the soul-ish, self-conscious part of us, we are sanctified progressively as our minds and behavior patterns are transformed (see Romans 12:2). The result is an increased conformity to the image of Christ (see Romans 8:29).
Back to my diagram. If I were more computer savvy, I'd cut and paste something as a visual aid for you. Unfortunately, however, I'm not that computer savvy.
In lieu of a visual aid, then, picture a typical, stylized heart, which represents the invisible aspect of personhood, which for our purposes consists of an admixture of spirit and soul. The physical body is, as it were, the agent of, or vehicle for, the spirit and/or soul. In a biblical hierarchy of values, however, the spirit as a sanctified mind must always trump the soul, particularly when the soul wants to use the body, via the mind/body nexus, as a vehicle for gratifying the desires of the flesh.
I suggest that the heart will always be divided. However, as we mature as Christians, becoming increasingly sanctified (or set apart) by God as vessels of honor, our spirits and our souls will increasingly cooperate with each other, so that our self-conscious self becomes increasingly our God-conscious self. As we increasingly submit, yield, and cooperate with God in His plan for our lives, we experience progression and spiritual maturity. Accordingly, the Spirit of God empowers us in the spiritual discipline of
"Casting down imaginations, and every high thing that exalteth itself against the knowledge of God, and bringing into captivity every thought to the obedience of Christ . . ." (2 Corinthians 10:5 KJV, my emphasis).