The story of Passover has its beginning in the days of Abraham.
When G-d promised Abraham (then still called Abram) an heir, whose seed would be as numerous as the stars, G-d also informed him at the same time of the long period of enslavement his children would endure for 400 years, until they would be liberated "with abundant substance."
First of Abraham's descendants to arrive in Egypt was Joseph, whose miraculous rise from slavery to the Viceroyalty is one of the most inspiring narratives of the Torah.
In the dramatic story of Joseph and his brothers we can clearly see the guiding hand of Divine Providence which led Jacob and his family cheerfully to Egypt.
The arrival of Jacob and his family in Egypt was a march of triumph. So was also the departure, 210 years later, of his children, the children of Israel, from Egypt a march of triumph.
There was this difference: the small family of seventy souls had become a great and unified nation of several million souls, of whom 600,000 adults (men only) marched forth "with a high hand."
The story of Passover, climaxed by Shavuot (with the Giving of the Torah on Mount Sinai), is the story of the birth of the "kingdom of priests and holy nation", our Jewish people.