Dis·cern·ment – the ability to judge well.
Hebrews 4:12 For the word of God is living and active, sharper than any two-edged sword, piercing to the division of soul and of spirit, of joints and of marrow, and discerning the thoughts and intentions of the heart.
Reality and healthy survival demands our being able to judge well to live well. That ability to judge well is what our Sovereign Judge, Resurrected Perfecter an Evidence of Truth have united to provide us. Defining the “division of soul and of spirit” requires more imagination than the grisly image Hebrews paints of a sword whacking through bone to reveal the living inner part, the marrow, that actually provides it needed nourishment.
Hebrews is saying the soul is like a boney structure we might identify as the biblical hard heart. The penetration of that boney structure has to happen to reveal the marrow, the Spirit, inside that hard heart. That allows the Spirit and the Word of God to become the needed nourishment of our growth, impact the intentions of our heart and teach us to judge well. It’s the total package.