A profound connection exists between absolute trust in God and the divine peace and protection granted to a faithful person. When an individual places complete reliance on God, they are met with a promise of deep, unwavering tranquility.
The primary approach among commentators [אבן עזרא, רד״ק, מצודת ציון ומלבי״ם] is that this trust begins in the mind, rooted in a person's thoughts, imagination, or the natural inclinations of the heart. It is a mindset firmly supported by God. A slightly different perspective suggests this refers specifically to the believer's will [ביאור שטיינזלץ]. However, another view argues against linking this state to active thought or planning [שד״ל]. According to this approach, a person who truly trusts in God sits in peace and does not need to constantly formulate plans. Instead, the focus is on the created being itself, meaning the very person God formed. Regardless of whether it is the mind, the will, or the whole person, this reliance is absolute. The individual leans on the Creator so heavily that they refuse to abandon their faith, even when confronted with severe fears and suffering [רש״י].
Because of this steadfast reliance, the individual is assured that God will guard and protect them [מצודת ציון]. This divine protection is characterized by an overwhelming, amplified sense of peace, guaranteeing an abundant tranquility that ensures the person will not be gripped by terror and will remain safe from all harm [רד״ק, מצודת דוד ושד״ל]. Offering a unique perspective, one commentator [מלבי״ם] suggests that the concept of peace here operates on two levels: first as a direct address to God Himself, who is known as Peace, and second as the resulting blessing. In this light, the meaning is that God, who is Peace, will guard the individual so they may experience true peace.
Ultimately, the reason for receiving such profound protection is the act of trust itself. Because the individual has placed their confidence in God alone, relying on no other source [שד״ל], it is only right and fitting that God extends His guardianship and grants them lasting serenity [רש י ומצודת דוד].