Seeing as Moshe told them nothing new, what is "v'iYdatem ha'Yom" referring to?
Rashi: It is referring to taking it to heart - to know and to understand, and to accept Hashem's rebuke. 1
Seforno: It is referring to the generation that is entering Eretz Kena'an, who witnessed all the forthcoming list of wonders firsthand, and who should therefore make signs 2 as testimony for the next generation who did not see it, to learn about them.
What are "Gadlo", "Yado ha'Chazakah" and "Zero'o ha'Netuyah" referring to?
Ramban #1 (citing the Ibn Ezra): 'To take you out of Egypt, the signs and the wonders that Hashem performed with Par'oh and those that He performed with you in the desert in connection with the Manna'. 1
Ramban #2: "Gadlo" refers to where Hashem revealed His superiority; 2 "Yado ha'Chazakah" to where He told Moshe (in Shemos, 3:20) "Veshlachti es Yadi Vehikeisi es Mitzrayim", and to the Yam-Suf where the Torah writes (in Beshalach, 14:31) "Vayar Yisrael es ha'Yad ha'Gedolah ... ": and "Zero'o ha'Netuyah" to the fact that, from the moment that Hashem stretched out His Hand against the Egyptians, He gave them no respite until He wiped them out at the Yam-Suf. 3
Seforno: "Gadlo" and "Yado ha'Chazakah," refer to 11:7:1:2. "Zero'o ha'Netuyah" refers to Hashem's outstretched Arm, which was ready to strike again if the sinner continued to sin.
The Ramban objects to this explanation since the Torah is currently concerned with the punishments with which Hashem chastised those who transgressed His Will. Refer also to 11:7:1:2.
Why does it say "Lo Es Beneichem
Da'as Zekenim, Hadar Zekenim: Your children are less liable to be punished than you, for you saw Hashem's chastising and His greatness. It does not come to exempt the children.