There is a deep human desire to record moments of monumental salvation, ensuring that gratitude to God echoes across future generations. Documenting miracles allows those who come later to connect with events they did not witness firsthand. The primary approach among commentators is that this refers to writing down the miracles of future redemption for the sake of generations who will not experience them directly [רש״י, רד״ק, מצודת דוד, ביאור שטיינזלץ]. This written record acts as a form of prophetic proof [אבן עזרא] and guarantees that the salvation will be remembered as eternal and unbroken [מאירי].
Other scholars suggest a more specific historical text. It may refer to the Scroll of Esther, which was documented to give the Israelites strength during their exile and prevent them from losing hope in ultimate redemption [אלשיך]. Another unique perspective suggests it hints at the Oral Torah. Although initially meant to be passed down by word of mouth, it was eventually written down to ensure it would never be forgotten by the Israelites throughout their long exile [חומת אנך].
When considering who will stand to praise God, the simplest understanding points to the future generations who will be born long after the events take place [רד״ק, מצודת דוד, ביאור שטיינזלץ]. However, a deeper conceptual view suggests that the ones praising God are the very Israelites who experience the redemption. The sudden, dramatic shift from slavery to freedom and from darkness to light is so profound that the people are essentially created anew, their youth and vitality completely restored [רש״י, אבן עזרא, מאירי].
Looking at this through a specific historical lens, this renewal perfectly describes the generation of Mordecai. Living under the threat of Haman's decree of total destruction, the Israelites were essentially considered dead. Their sudden rescue was nothing short of a literal rebirth. Consequently, they direct their praise using a specific name of God, a name that symbolizes His eternal war against the nation of Amalek, the very lineage from which Haman descended [אלשיך].