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 -- they would be enslaved for 400 years, at the end of which they would be liberated "with abundant wealth."
The first of Abraham's descendants to arrive in Egypt was Joseph, whose miraculous rise from slave to the viceroy 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 bringing Jacob and his family cheerfully to Egypt.
The arrival of Jacob and his family in Egypt was a march of triumph. So was the departure, 210 years later, of his children, the children of Israel, from Egypt.
There was this difference: the small family of seventy souls had become a great and unified nation of several million souls (the count of 600,000 includes only the adults men) who marched forth "with a high hand."
The story of Passover, which reaches its climax at 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.