True trust in God is invisible to the human eye, resting entirely within a person's inner intentions. Often, an individual may outwardly perform good deeds and speak words of faith, yet harbor a mind that is entirely detached from those actions [רד״ק, צאינה וראינה]. This disconnect explains why some people who appear to rely on God do not find success; their trust is superficial, spoken only from the lips rather than rooted in the depths of their soul [מלבי״ם].
The human heart is fundamentally distorted and full of deceit [מצודת ציון, ביאור שטיינזלץ]. It is considered more crooked than any other part of the body [מצודת דוד], constantly brimming with excuses and negative thoughts [רש״י]. Because a person can so easily mask their true motives through speech and outward behavior, the heart serves as the ultimate and deepest source of all trickery [רד״ק]. Beyond mere distortion, the heart is also a place of ambush, perpetually surrounded by desires and negative traits that lie in wait to seize control of the soul [מלבי״ם].
The primary approach among commentators is that the heart suffers from a profound sickness, characterized by severe pain and brokenness. This illness manifests as constant worries, sorrow, harmful thoughts, and a corrupted state of mind [רש״י, רד״ק, מצודת ציון, מצודת דוד, ביאור שטיינזלץ]. Conversely, another perspective views this condition as a reflection of basic human nature, pointing out that the heart is incredibly unstable. It is subject to endless fluctuations, capable of shifting at any moment based on whatever thoughts or images currently dominate it [מלבי״ם].
Because of this deep complexity, people often fall into the trap of thinking their inner conscience is completely hidden, assuming no one will ever know if their trust in God is genuine [רש״י, מצודת דוד]. From a strictly human standpoint, this is true. It is impossible to determine another person's true character based merely on outward appearances. The heart is so profoundly deceptive that individuals often fool themselves, unaware of their own true essence and unable to tell if their lives are driven by genuine faith or mere desires [מלבי״ם, ביאור שטיינזלץ]. Yet, despite this complete human limitation, God actively searches the hearts of people, possessing perfect knowledge of every hidden secret within the soul [רש״י, רד״ק, צאינה וראינה].