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 neighbour 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 judgements: 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. 

Alternate

A reading from the Book of Joshua (2:1-4, 6, 12-13, 17, 21)

Joshua son of Nun secretly sent two spies from Shittim. “Go, look over the land,” he said, “especially Jericho.” So they went and entered the house of a prostitute named Rahab and stayed there. The king of Jericho was told, “Look, some of the Israelites have come here tonight to spy out the land.” So the king of Jericho sent this message to Rahab: “Bring out the men who came to you and entered your house, because they have come to spy out the whole land.”

But the woman had taken the two men and hidden them. She said, “Yes, the men came to me, but I did not know where they had come from. (But she had taken them up to the roof and hidden them under the stalks of flax she had laid out on the roof.)

 “Agreed,” she replied. “Let it be as you say.”

So she sent them away, and they departed. And she tied the scarlet cord in the window.

RESPONSORY

From the “Dialogue with Trypho” by St. Justin Martyr (+165)

The blood of the passover, sprinkled on each one's door-posts and lintel, delivered those who were saved in Egypt, when the first-born of the Egyptians were destroyed. For the passover was Christ, who was afterwards sacrificed, as also Isaiah said, 'He was led as a sheep to the slaughter.' And it is written, that on the day of the passover you seized Him, and that also during the passover you crucified Him. And as the blood of the passover saved those who were in Egypt, so also the blood of Christ will deliver from death those who have believed. Would God, then, have been deceived if this sign had not been above the doors? I do not say that; but I affirm that He announced beforehand the future salvation for the human race through the blood of Christ. For the sign of the scarlet thread, which the spies, sent to Jericho by Joshua, son of Nave (Nun), gave to Rahab the harlot, telling her to bind it to the window through which she let them down to escape from their enemies, also manifested the symbol of the blood of Christ, by which those who were at one time harlots and unrighteous persons out of all nations are saved, receiving remission of sins, and continuing no longer in sin.