Total Freedom
The Jewish people left Egypt on the fifteenth of Nissan, corresponding to the first day of Pesach. This took place 2448 years of creation. Since we are now in the year 5786, this was 3338 years ago.
The exodus represented an end to the bondage and suffering. The Jewish people were not stress free until the seventh day of Passover with the splitting of the Red Sea. Once the Egyptians drowned in that miraculous event, it was clear that they would never be a threat again.
This is what makes the seventh day of the holiday so special. On the one hand, one of the greatest nature defying miracles occurred on this day, but it also represented that we were truly a nation that was free.
The Kuzari points out that this event is evidence to the truth of the Torah. The proof is that it is acknowledged by the great religions of the world, that it is an event that actually occurred.
Of all of the great miracles that we experienced as a people, only קריעת ים סוף, is an integral part of our morning prayers every day of the year.
It represented the moment when we were a free and independent people. And it was a reminder of how Hashem openly revealed Himself in an undisputed manner. No religion ever began in such a wondrous fashion. This is because Judaism is the one and only true religion.
This Pesach, the seventh day should equally represent our being rid of the threat of our enemies once and for all.