While telling the Corinthians to put out an unrepentant man from their assembly, Paul says a little contaminant is like yeast; it spreads through the whole lump of dough.  As he writes to the Corinthians, who were just coming out of paganism, he states how they should apply this understanding to their keeping of the Festival of Unleavened Bread.

1Cor 5:7 (KJS) Purge out therefore the old leaven, that ye may be a new lump, as ye are unleavened. For even Messiah our passover is sacrificed for us:
8 Therefore let us keep the feast, not with old leaven, neither with the leaven of malice and wickedness; but with the unleavened [bread] of sincerity and truth.

Messiah explained his use of the word leaven.

Matt 16:6 (KJS) Then Yahshua said unto them, Take heed and beware of the leaven of the Pharisees and of the Sadducees.
Matt 16:11 (KJS) How is it that ye do not understand that I spake [it] not to you concerning bread, that ye should beware of the leaven of the Pharisees and of the Sadducees?
12 Then understood they how that he bade [them] not beware of the leaven of bread, but of the doctrine (contaminating doctrine) of the Pharisees and of the Sadducees.

So leaven is contamination.
And I Cor. 5:7 could be read like this:

**1Cor 5:7 Therefore get rid of your contamination, so that you may be like a new lump of dough, uncontaminated. Remember, the Messiah is the Passover sacrificed for us (to atone for us and cleanse us from contamination).
8 Let us keep the Festival without the old contaminants of malice and wickedness, but with bread without contamination, bread of sincerity and truth.**

Paul’s statement confirms that we should be keeping the following commandment:

Exod 23:14 (KJS) Three times thou shalt keep a feast unto me in the year.
15 Thou shalt keep the feast of UNLEAVENED BREAD: (thou shalt eat unleavened bread seven days, as I commanded thee, in the time appointed of the month Abib; for in it thou camest out from Egypt: and none shall appear before me empty:)
16 And the FEAST OF HARVEST, the firstfruits of thy labours, which thou hast sown in the field: and the FEAST OF INGATHERING, [which is] in the end of the year, when thou hast gathered in thy labours out of the field.

And as Paul confirms keeping the commandment, he instructs the readers to keep contaminating doctrines from mixing in, and to acknowledge the new covenant in the Messiah’s blood (the Messiah being our Passover also means no more animal sacrifice for sin).

Let’s go back for a few minutes and look at the Exodus.

Exod 12:21 (NIV) Then Moses summoned all the elders of Israel and said to them, Go at once and select the animals for your families and slaughter the Passover lamb.  Take a bunch of hyssop, dip it into the blood in the basin and put some of the blood on the top and on both sides of the door frame. Not one of you shall go out the door of his house until morning.  When [Yahweh] goes through the land to strike down the Egyptians, he will see the blood on the top and sides of the door frame and will pass over that doorway, and he will not permit the destroyer to enter your houses and strike you down.
Exod 12:42 (NIV) Because Yahweh kept vigil that night to bring them out of Egypt, on this night all the Israelites are to keep vigil to honor Yahweh for the generations to come.
Not leaving their homes until morning, as they were instructed; they then spoiled the Egyptians as they traveled through Rameses and left Egypt.
Numb 33:1 (KJS) These [are] the journeys of the children of Israel, which went forth out of the land of Egypt with their armies under the hand of Moses and Aaron.
2 And Moses wrote their goings out according to their journeys by the commandment of Yahweh: and these [are] their journeys according to their goings out.
3 And they departed from Rameses in the first month, on the fifteenth day of the first month; on the morrow after the passover the children of Israel went out with an high hand in the sight of all the Egyptians.
Rameses was apparently along the road they had to use to leave Egypt.  Through here the Israelites passed toward Succoth.
Exod 12:37 (KJS) And the children of Israel journeyed from Rameses to Succoth, about six hundred thousand on foot [that were] men, beside children.
38 And a mixed multitude went up also with them; and flocks, and herds, [even] very much cattle.
39 And they baked unleavened cakes of the dough which they brought forth out of Egypt, for it was not leavened; because they were thrust out of Egypt, and could not tarry, neither had they prepared for themselves any victual.

Looking at the Festival of Unleavened Bread today
While that Passover night was a frightening event, the children of Israel were now rejoicing because they were leaving the bonds of slavery.  They were happy to be set free.  And today, although we are solemn at Passover because of the suffering and death of the Messiah for us as our Passover lamb; we are happy that the festival of Unleavened Bread points to a day when we will not have to live under this Egyptian or world system.

Just as the children of Israel had difficulty living their beliefs in Egypt, we have difficulty living our beliefs in today’s world.  Those in charge were not righteous then and those in charge are not righteous now.

Since the Egyptians hurried them to leave, they had no time to stop and leaven their breads and wait for it to rise, they had to make do with unleavened bread (Exo. 12:34).  Yahweh set this to be used later as a reminder that there are some things we cannot take with us when we decide to serve him, because they spread out and contaminate.  Once leaven or yeast is in the dough, you cannot get it out.  Messiah tells us that leaven represents doctrines or teachings.  A doctrine of error, once entered into an assembly, quickly spreads unless all know the Scriptures well.  Sometimes a doctrine of error cannot be removed from an assembly once it spreads, and the assembly is forever contaminated.  Those who still have not accepted the error usually leave and then the assembly is 100% corrupt!

So we are reminded, by removing leaven from our home and eating the unleavened bread, to only eat (swallow) doctrine that is truth.  We must rid ourselves of erroneous teachings by diligent study and commitment.  We should constantly work to keep our doctrines accurate and pure to the Scriptures.  We must not subtract or add to the guidance that Yahweh has given us.

The first day of the feast (festival) of Unleavened Bread can be seen as the day we repented and began our journey to leave the doctrines of the world.  As the children of Israel proceeded to the promised land, they were to drop the errors, false teachings and unrighteous ways in the desert.  The path through the desert, symbolically should have been littered with things discarded  from their lives.  So this week should be a lesson to us, a reminder each time we eat a piece of unleavened bread, to discover what we should discard in our walk toward the promised land.  It may be an unrighteous thing in our attitude or behavior.  It may be a doctrine (teaching) that we picked up previously, but that we cannot clearly prove by Scripture.

The last day of the feast (festival) of Unleavened Bread represents finally breaking free from the oppression of the world system.  This was when the children of Israel stepped on the far shore of the Red Sea and couldn’t be touched by Pharaoh’s army. Now the battle was within themselves. Let us be committed to win this internal battle with the power given to us by Yahweh through immersion in his Ruach HaKodesh (Set-apart Breath).  Let us study diligently and remove contaminants from ourselves and from our doctrines.