"why is this night different from all other nights...?"
‘I am Adonai. I will free you ... rescue you from their oppression, and redeem you with an outstretched arm and with great judgments. I will take you as my people, and I will be your God. Then you will know that I am Adonai your God..' Ex 6.6
On that day you are to tell your son, ‘It is because of what Adonai did for me when I left Egypt.’