Trapped between the crashing waves of the sea and the advancing Egyptian army, the Israelites face a moment of absolute terror. Having left Egypt armed, they anticipate a physical battle and are completely overwhelmed by the massive size of the enemy forces [העמק דבר]. Instead of organizing for war or giving in to despair, Moses introduces a revolutionary approach to their survival. The people are told to remain completely passive and rely entirely on God. God will not merely assist them in a military campaign; He will manage and execute the entire battle from beginning to end on their behalf, removing any reason to fear the Egyptian army [רש״י, אבן עזרא, ביאור יש״ר, אור החיים, ביאור שטיינזלץ].
The primary approach among commentators is that this conflict is not the Israelites' fight at all, but rather God's personal war. Because the Egyptians witnessed the devastating plagues in Egypt and still chose to pursue their former slaves, they are essentially challenging God directly [רבנו בחיי, מלבי״ם, צאינה וראינה]. Even as God enacts strict justice to destroy the pursuing army, He weaves in His mercy. This divine compassion is evident in the fact that the Egyptians are ultimately granted the dignity of burial [רבנו בחיי, שפתי כהן]. Furthermore, God's direct intervention turns what could be an overwhelming moment of strict judgment into an act of pure mercy for the Israelites [אור החיים].
In stark contrast to the cries of panic, war shouts, and complaints the people voiced moments earlier, Moses demands total silence [אבן עזרא, חזקוני, בכור שור, ביאור יש״ר, שד״ל]. This requirement for complete quiet operates on several distinct levels. Practically, it serves a tactical purpose: by remaining silent, the Israelites prevent the nearby Egyptian forces, who are camped nearby under the cover of a cloud, from locating them and firing arrows in the dark [רלב״ג]. Spiritually, the silence acts as a necessary defense. Because the Israelites were also involved in sin and idolatry while in Egypt, speaking out could draw strict judgment upon themselves, potentially equating their guilt with that of their enemies [רבנו בחיי, שפתי כהן, צאינה וראינה].
Ultimately, this requested silence represents the highest form of deep trust. Moses asks the people to cease even their prayers and shouts. At certain crucial moments, an act of silent, unwavering faith holds far greater merit than crying out to God [בעל הטורים, ברכת אשר, קאסוטו]. Yet, even if the people have reached a point of total exhaustion where they completely lack the strength to pray, they are assured that God will still step in and fight for them [אור החיים].