משלי, פרק י״ד, פסוק ל׳

A person's mental and emotional state directly shapes their physical strength. There is a sharp contrast between two opposite inner conditions: inner peace on one hand, and jealousy or anger on the other. Each state leaves a profound mark on the human body, affecting everything from the outer flesh to the deepest bones.

The primary approach among commentators is that the heart serves as the ultimate source of life and health for the entire body. It actively heals the flesh and provides it with life [מלבי״ם]. This healthy state is also understood as one of deep relaxation and letting go [מצודת ציון]. It reflects an individual with a good, joyful, and peaceful heart, entirely free from negative traits and excessive desires [אבן עזרא, אמרי דעת]. Such a person easily forgives, refuses to hold a grudge, releases anger, and does not covet what belongs to others, thereby bringing life to God's creations [רש״י, רלב״ג, עמנואל הרומי]. By living without constant worry and avoiding thoughts of revenge, they grant their body lasting vitality and robust health [מצודת דוד, שטיינזלץ].

In stark contrast is the physical ruin caused by negative emotional states. The destructive emotion of jealousy takes the form of intense anger, wrath, and deep-seated resentment [רש״י, מצודת ציון], or a continuous sorrow over the success and good fortune of others [עמנואל הרומי]. Naturally, the heart is meant to pump life throughout the body, but allowing jealous thoughts to enter completely disrupts this positive function [אלשיך, מלבי״ם]. Because there will always be people enjoying good fortune in the world, the jealous person is trapped in an endless cycle of sorrow and anxiety. This constant tension goes beyond merely harming the flesh. It triggers a deep, destructive process of decay within the bones themselves, ultimately crumbling a person's inner core and consuming their entire body [עמנואל הרומי, מצודת דוד, שטיינזלץ].