The LORD said to Moses and Aaron in the land of Egypt: This month shall mark for you the beginning of months; it shall be the first month of the year for you. Tell the whole congregation of Israel that on the tenth of this month they are to take a lamb for each family, a lamb for each household. If a household is too small for a whole lamb, it shall join its closest neighbor in obtaining one; the lamb shall be divided in proportion to the number of people who eat of it. Your lamb shall be without blemish, a year-old male; you may take it from the sheep or from the goats. You shall keep it until the fourteenth day of this month; then the whole assembled congregation of Israel shall slaughter it at twilight. They shall take some of the blood and put it on the two doorposts and the lintel of the houses in which they eat it. They shall eat the lamb that same night; they shall eat it roasted over the fire with unleavened bread and bitter herbs. Do not eat any of it raw or boiled in water, but roasted over the fire, with its head, legs, and inner organs. You shall let none of it remain until the morning; anything that remains until the morning you shall burn. This is how you shall eat it: your loins girded, your sandals on your feet, and your staff in your hand; and you shall eat it hurriedly. It is the passover of the LORD. For I will pass through the land of Egypt that night, and I will strike down every firstborn in the land of Egypt, both human beings and animals; on all the gods of Egypt I will execute judgments: I am the LORD. The blood shall be a sign for you on the houses where you live: when I see the blood, I will pass over you, and no plague shall destroy you when I strike the land of Egypt. This day shall be a day of remembrance for you. You shall celebrate it as a festival to the LORD; throughout your generations you shall observe it as a perpetual ordinance. Seven days you shall eat unleavened bread; on the first day you shall remove leaven from your houses, for whoever eats leavened bread from the first day until the seventh day shall be cut off from Israel. On the first day you shall hold a solemn assembly, and on the seventh day a solemn assembly; no work shall be done on those days; only what everyone must eat, that alone may be prepared by you. You shall observe the festival of unleavened bread, for on this very day I brought your companies out of the land of Egypt: you shall observe this day throughout your generations as a perpetual ordinance. In the first month, from the evening of the fourteenth day until the evening of the twenty-first day, you shall eat unleavened bread. For seven days no leaven shall be found in your houses; for whoever eats what is leavened shall be cut off from the congregation of Israel, whether an alien or a native of the land. You shall eat nothing leavened; in all your settlements you shall eat unleavened bread. Then Moses called all the elders of Israel and said to them, “Go, select lambs for your families, and slaughter the passover lamb. Take a bunch of hyssop, dip it in the blood that is in the basin, and touch the lintel and the two doorposts with the blood in the basin. None of you shall go outside the door of your house until morning. For the LORD will pass through to strike down the Egyptians; when he sees the blood on the lintel and on the two doorposts, the LORD will pass over that door and will not allow the destroyer to enter your houses to strike you down. You shall observe this rite as a perpetual ordinance for you and your children. When you come to the land that the LORD will give you, as he has promised, you shall keep this observance. And when your children ask you, ‘What do you mean by this observance?’ you shall say, ‘It is the passover sacrifice to the LORD, for he passed over the houses of the Israelites in Egypt, when he struck down the Egyptians but spared our houses.’” And the people bowed down and worshiped. The Israelites went and did just as the LORD had commanded Moses and Aaron. (Exodus 12:1-28, NRSV)
Here is Lord explaining the festival of Passover. How it was done the first time when the spirit of Death moved over Egypt and killed the first born male. You need to be prepared to move. Kill a lamb and if the family is not big enough for a lamb, then share. There can be no leftovers, as we will be moving quickly. Eat with your shoes on and dressed.
Remember how God saved us. Remember.