Human emotions are never strictly confined to the mind. They carry a profound physical weight, directly shaping a person's health, vitality, and physical appearance. The physiological and psychological contrast between joy and sadness reveals how deeply our inner feelings dictate our physical reality.
A person who is happy with their lot in life, avoiding anger over meaningless worldly pursuits, experiences a direct physical benefit [רש״י, אבן עזרא]. The primary approach among commentators views this type of joy as an actual medicine, acting within the body as a healing agent that actively promotes health [אבן עזרא, מצודת ציון, מצודת דוד, ביאור שטיינזלץ]. Other perspectives suggest that this inner happiness radiates outward like light, visibly improving a person's face [עמנואל הרומי, רש״י], or directly strengthening the external body itself [מלבי״ם]. Physiologically, happiness expands the spirit, spreading blood and natural heat throughout the organs, which floods the body with strength and vitality [רלב״ג, אמרי דעת].
Conversely, a broken, depressed, and sad spirit triggers the exact opposite physical reaction [מצודת ציון, ביאור שטיינזלץ]. Sadness draws the body's blood and natural heat inward, away from the limbs, diminishing a person's natural life force. This internal retreat literally dries out the bones, which serve as the vital foundation and core of the human body [אבן עזרא, מצודת ציון, ביאור שטיינזלץ]. As sadness drains the moisture from the bone marrow and the flesh [מצודת דוד, עמנואל הרומי], it creates a state of internal damage so deep that no external medicine can possibly cure it [אבן עזרא].
Beyond the physical mechanics of emotion, there is a deeper distinction between a person's outer life and their inner essence. In this framework, the heart represents the external, material vessel, while the spirit embodies the true inner self. It is entirely possible for someone to achieve material success and experience a surface-level happiness that improves their outward appearance. However, if their inner spirit remains broken and depressed, that internal sadness will still dry out their bones and destroy their true foundation. Ultimately, the true measure and health of a human being lie entirely in their inner spiritual state [מלבי״ם, אלשיך].