We find the first mention of Passover (or Pesach) in the Book of Exodus. We are told that the Children of Israel were slaves in Egypt, ruled by a cruel Pharoah. Taking pity on His people, G-d appeared to Moses in a burning bush and told him to lead the Jews out of slavery. When Pharoah refused Moses' pleas to release the Jews, G-d sent one plague after another upon the Egyptians until the Hebrews were allowed to leave. He opened a path through the Red Sea so that the people could escape.
The story is re-told every year in the Seder on the first and second nights of the holiday. During the days of Passover Jews eat no leavened foods, to commemorate the Hebrews who left Egypt in such a hurry that there was no time for their bread to rise.
The large stained-glass window in Kol Emeth's sanctuary is a depiction of the burning bush, and thus a reminder of our emancipation as a people and as individuals.