3 On the tenth day of this month, every family must select an unblemished, first-year, male lamb or goat. 6 On the evening of the fourteenth day, kill the animal and wipe some of its blood on the sides and top of the door posts.
12 I will pass through Egypt, killing all the firstborn men and animals. 13 As I pass over Egypt, I'll see the blood on your door posts, and I'll pass over you. That way I'll know not to kill your firstborn men or animals.
God continued his speech, saying,
14 This day shall be a memorial to you. You must keep it by law forever.
15 For seven days you must eat unleavened bread, and you must remove all leaven from your houses.
Whoever eats leaven bread during this time must be cut off from Israel.
16 There will be holy convocations on the first and seventh days.
The Israelites went from a population of only seventy (Exodus 1:5) to several million (600,000 men) in a few hundred years.
If there were 3 million Israelites marching rows of families with an average of five members with a meter between the rows, the column would have stretched 600 km -- which is more than the distance between Goshen and Jerusalem.