In preparation, they were to remove every speck of leaven (a picture of sin) from their homes.
Exodus 12:18 In the first month, on the fourteenth day of the month at even, ye shall eat unleavened bread, until the one and twentieth day of the month at even.
19 Seven days shall there be no leaven found in your houses: for whosoever eateth that which is leavened, even that soul shall be cut off from the congregation of Israel, whether he be a stranger, or born in the land.
20 Ye shall eat nothing leavened; in all your habitations shall ye eat unleavened bread.
On the night of the fourteenth of Nissan, the night before the Passover seder, an intentional, ritual search of the house is performed. To do this, these items are needed: a candle, a feather (or toothbrush), a wooden spoon, and a piece of cloth (or a small paper bag). It is customary to place items of chametz (something that doesn’t make crumbs) in ten different places in the house, so that the searcher will actually find something. A child can be given the task of hiding the chametz.
All the lights in the house are turned off, and the candle is lit. Since it is a mitzvah to remove the leaven, it is begun with a blessing:
“Blessed are You, Lord our God, King of the Universe, Who sanctified us with His commandments, and commanded us concerning the removal of leaven.”
Every corner of the house is searched by candlelight. When chametz is found, it is swept onto the spoon with the feather, and then put in the cloth or bag.
After all of the chametz has been found, this declaration is made:
“All manner of leaven that is in my possession, that which I have not seen, and that which I have not removed, shall hereby be annulled, and accounted as the dust of the earth.”
The next morning, chametz may no longer be eaten. The cloth bag of chametz, along with the feather and the spoon are burned outside. Before burning, this declaration is made:
“All manner of leaven that is in my possession, that which I have seen and that which I have not seen, that which I have removed, and that which I have not removed, shall hereby be annulled and accounted as the dust of the earth.”-Passoverleavensederunleavened breadchametzkosher for Passover
Now, did the removing of leaven cover their sins? No, it was the blood of the lamb that God looked at, and yet he still commanded them to remove the leaven before the blood was applied.
Exodus 12:21 Then Moses called for all the elders of Israel, and said unto them, Draw out and take you a lamb according to your families, and kill the passover.
22 And ye shall take a bunch of hyssop, and dip it in the blood that is in the bason, and strike the lintel and the two-side posts with the blood that is in the bason; and none of you shall go out at the door of his house until the morning.
23 For the LORD will pass through to smite the Egyptians; and when he seeth the blood upon the lintel, and on the two side posts, the LORD will pass over the door, and will not suffer the destroyer to come in unto your houses to smite you.
24 And ye shall observe this thing for an ordinance to thee and to thy sons for ever.
It is the same today. God still commands us to repent of our sins and rebellion toward him and to put our faith in Christ, the crucified lamb of God.