The 7th Day of Pesach is when the sea split, *the "waters broke"* so to speak, and the birth of the Jewish nation was completed.
The awareness of G-d we saw that night was unlike anything before, and greater than even what the Prophet Ezekiel saw.
It is what enabled us to receive the Torah weeks later at Mount Sinai, and it gave us a foretaste of the awareness of G-d that will be revealed in the time of Mashiach and Geulah (final redemption from exile)!
The 7th day of Pesach begins tonight!
The energy of this day happens now too, and what that means is the gates of heaven are open like at Neilah on Yom Kippur, and we can ask for and elicit great blessings from above.
Thus the custom to stay up this night to learn Torah.