“For the word of God is living and active and full of power [making it operative, energizing, and effective]. It is sharper than any two-edged sword, penetrating as far as the division of the soul and spirit [the completeness of a person], and of both joints and marrow [the deepest parts of our nature], exposing and judging the very thoughts and intentions of the heart.”
“Hebrews 4:12 In addition to “sword,” the word in Greek was used for the knife used by the priests to slit the throats of the sacrificial lambs and for the knife (scalpel) used by a surgeon.” – The Amplified Bible
Note that when the priest’s knife would cut through the bone, the joints were distinct from the marrow. (Modern science observes the marrow to be the inner, life-giving element) . So bone was the unifying structure with joints and marrow being distinct, not just in connotation, but in reality and function. Similarly, the immaterial part of a person (like bone) is one, yet comprised of soul (joints) and spirit (marrow). And only the Word of God reveals and penetrates theses distinctions; (Augustinian theology certainly does not.)
“Hebrews 4:12 apparently indicates that soul and spirit are to be distinguished though there is difficulty in doing so. The distinction is often defined in terms of the higher and lower aspects of man’s psychical life; the soul is said to be the manifestation of the immaterial part of man toward the world, and the spirit its manifestation toward God. 1 Corinthians 2:14, 15, makes the clearest distinction between psychikoi [soulical] as men whose lives are uninfluenced by the Holy Spirit [unregenerated], and pneumatikoi [spiritual] as those who are directed by the Spirit of God (cf. Jude 19) [and regenerated by the Spirit of God – John 3:3-6]. – Encyclopedia of the Bible, “Spirit.”
This is the view of holistic trichotomy: man’s primary nature is one, having two separable elements (2 Cor. 5:8), yet man’s immaterial side has two distinguishable aspects/dimensions (1 Thess. 5:23).