God's careful watch constantly follows the righteous, ensuring their fundamental well-being despite the inevitable hardships and suffering they may face in life. God acts as a steady guardian, actively protecting them from ultimate harm [רש״י].
When exploring how this protection works, the primary approach among commentators focuses on the structural core of a person. Bones represent the essential foundations and pillars that support the human body [רד״ק, אבן עזרא, מאירי]. The promise here is that even when a righteous person falls, suffers bruises, or endures numerous troubles, their central core will never sustain heavy damage. Much like a tree whose branches might be battered by a storm, their roots and foundations will remain completely stable and intact [אבן עזרא, מאירי, שטיינזלץ, אלשיך]. This security is absolute, guaranteeing that not even a single piece of this core foundation is shattered [מצודת ציון].
Beyond the physical safety granted in this world, this divine protection extends into the afterlife. While only one small bone is strictly necessary to rebuild a body for the future resurrection, God goes much further. Because of the deep holiness of the righteous, He preserves all of their bones in the grave, keeping them completely safe from decay [אלשיך].