My great-great grandfather, the Bnei Yissaschar, points out the while there are many miracles recorded in TANACH, we do not commemorate or celebrate them all. Thus, we do not commemorate Yehoshua's stopping the sun, or his splitting of the Jordan River, 40 years after Moshe split the Red Sea. On the other hand, we commemorate the miracles of Pesach, Succot, Shavuot, and also Chanuka and Purim, two post-Biblical miracles.

 

What determines which miracles we commemorate and which we do not? The Bnei Yissaschar answers that there are miracles whose influence was a one time historical event, with no continued influence for the future. These miracles we do not commemorate or celebrate. Then there are miracles whose influence is eternal, i.e. the day of that date, whenever it arrives again, is eternally imbued with the same influence that was granted to it when the miracle first occurred. Thus, we say in the Bracha for Chanuka and Purim, "He who performed miracles for our fathers in those days at this time". This means that the Holy Light of the Shechina which was revealed "in those days", is present again, "at this time". He points out that the Sephardi version of this Bracha actually has it "and also at this time", i.e. the light of this miracle appeared then, and again now.

 

Thus, we thank Gd specifically for the "time of the miracle", when that time comes around again and again on the calendar. Each year, as we approach the commemoration of our first redemption from Egypt, when we became a nation, we wish to connect to the influence and power of that redemption.

 

The full benefit of Pesach is derived from seeing the Festival not only  as a commemoration of redemption, but also as a time of redemption. As the Zohar says, the First Redemption from Egypt is the Roadmap to the Final Redemption of Mashiach