Who will say so?
Rashi: His nation.
Why do they say "Hine Elokeinu Zeh Kivinu Lo"?
Ta'anis 31a: In the future, Hashem will make a dance for Tzadikim. He will sit among them in Gan Eden. Everyone will point at Him with the finger, and say "Hine Elokeinu Zeh..."
Malbim: The Nochrim used to say 'where is your G-d [to whom you hope for salvation]?! We will say, this is Elokeinu. We did not hope to Him in vain!
Why do they say "Elokeinu Zeh Kivinu Lo" and also "Zeh Hashem Kivinu Lo"?
Radak: The matter is repeated.
Malbim: Elokeinu to whom we hoped, He is Hashem who created all of existence. Automatically, His salvation is unlike salvation via nature or other means; they are not permanent.
Why do they say "Nagilah v'Nismecha bi'Yeshu'aso"?
Malbim: The salvation will be wondrous, in a way that arouses joy to one who hears of it. Also, it will be permanent.
