Fully aware that Jericho's destruction is certain, Rahab takes decisive action to secure survival for herself and her family. Having already hidden the Israelite spies and saved their lives, she demands a firm, binding guarantee of safety during the upcoming conquest.
Her request is driven by a critical sense of urgency, as action must be taken immediately before the city falls [מצודת דוד]. Establishing this agreement before the Israelites even cross the Jordan River or begin the war serves a vital legal and spiritual purpose. This specific timing allows Rahab to embrace belief in God and convert, thereby removing herself from the strict prohibition against leaving the Canaanite inhabitants alive [מלבי״ם, צווארי שלל, חומת אנך]. Securing the oath at this exact moment also prevents the spies from backing out later. If they delayed, the spies might eventually claim they were acting under duress and attempt to legally cancel their vow [ראשון לציון]. Interestingly, some explain that Rahab was able to assist the spies so freely because she did not actually belong to the local nation, and therefore was not bound by the decrees of Jericho's king [אהבת יהונתן].
When Rahab demands that the spies swear by God, the primary approach among commentators is that she is intentionally formulating an unbreakable vow. She establishes three specific conditions to lock in this commitment: the oath is made strictly on her terms, it invokes the explicit name of God, and it is grounded in the tangible benefit the spies have already received from her. When an oath is constructed under these precise circumstances toward someone who has already provided a vital favor, it becomes absolute and impossible to annul [מלבי״ם, צווארי שלל, ראשון לציון, חומת אנך].
A careful distinction is made between Rahab's own survival and the rescue of her relatives. Rahab does not ask for an act of unearned kindness regarding her own life. Since she saved the spies first, her survival is viewed as a basic obligation, a matter of truth and proportional justice. True kindness, which involves doing a favor for someone who has not earned it, is requested solely for her family. Her logic is clear: just as she performed an unearned kindness for the spies, they should perform an unearned kindness for her father's household [רד״ק, מצודת דוד, אלשיך]. Additionally, because she saved the lives of two men, she feels it would be unjust to survive completely alone. Lacking a husband and children, she asks that her father and brother be spared in exchange for the two spies she rescued, emphasizing that she is only asking for their lives, not their property [אברבנאל].
To finalize the agreement, Rahab requires a reliable sign. This serves as a practical, agreed-upon physical marker that the Israelites will use to identify her home and pass over it during the chaos of the conquest [רש״י, מצודת דוד, מלבי״ם, ביאור שטיינזלץ, אלשיך]. Beyond its practical use, it stands as a symbol of their sincere pledge, guaranteeing that they will not deceive her or break their covenant [רד״ק, צאינה וראינה, אברבנאל].