ישעיהו, פרק נ״ה, פסוק י״א

God's promises operate in the world with absolute certainty, leaving a permanent mark much like rain that fertilizes the earth. His spoken word acts as a messenger sent on a specific mission into the human realm. While a human messenger might fail or return without finishing the task, the Divine word always achieves its exact purpose [מצודת דוד, שד״ל, ביאור שטיינזלץ]. The primary approach among commentators is that this Divine speech refers directly to the prophecies and promises of redemption from exile, which were delivered to the people by the prophets [רש״י, רד״ק, אבן עזרא, צאינה וראינה]. These promises carry an absolute condition of fulfillment. They are guaranteed to leave a lasting impact, emphasizing the certainty that no obstacle or harm can delay or cancel even the smallest fraction of God's promise [רד״ק, מצודת דוד].

Alongside this guarantee, there is a deep condition tied to human choice. God's promises are designed to bring goodness to humanity, but fully experiencing them requires people to listen and prepare themselves [רש״י]. This introduces a unique angle to the messenger comparison. When a person sends a gift to a friend through a messenger, the messenger returns to the sender empty-handed if the friend accepts the gift. However, if the friend refuses it, the messenger must return with the gift still in hand. The same is true for Divine abundance sent into the world. If people prepare themselves and are worthy to receive it, the Divine messenger returns empty-handed because the blessing remains with the recipients. But if they are unprepared, the abundance is not received and returns directly to God [מלבי״ם].