'Leaven' in the Bible

[In the celebration of the Passover in future years,] seven days you shall eat unleavened bread, but on the first day you shall remove the leaven from your houses [because it represents the spread of sin]; for whoever eats leavened bread on the first day through the seventh day, that person shall be cut off and excluded from [the atonement made for] Israel.

Seven days no leaven shall be found in your houses; whoever eats what is leavened shall be cut off and excluded from [the atonement made for] the congregation of Israel, whether a stranger or native-born.

Unleavened bread shall be eaten throughout the seven days; no leavened bread shall be seen with you, nor shall there be leaven within the borders of your territory.

“You shall not offer the blood of My sacrifice with leavened bread, nor shall the sacrifice of the Feast of the Passover (Unleavened Bread) be left over until morning.

‘No grain offering that you bring to the Lord shall be made with leaven, for you shall not offer up in smoke any leaven [which symbolizes the spread of sin] or any honey [which, like leaven, is subject to fermentation] in any offering by fire to the Lord.

As an offering of first fruits you may offer them [leaven and honey] to the Lord, but they shall not go up [in smoke] on the altar as a sweet and soothing aroma.

What is left of it Aaron and his sons are to eat. It shall be eaten as unleavened bread in a holy place; they are to eat it in the courtyard of the Tent of Meeting.

It shall not be baked with leaven [which represents corruption or sin]. I have given it as their share of My offerings by fire; it is most holy, like the sin offering and the guilt offering.

Then Moses said to Aaron, and to his surviving sons, Eleazar and Ithamar, “Take the grain offering that is left over from the offerings by fire to the Lord, and eat it unleavened beside the altar, for it is most holy.

You shall bring in from your places two loaves of bread as a wave offering, made from two-tenths of an ephah of fine flour; they shall be baked with leaven as first fruits to the Lord.

For seven days no leaven shall be seen with you in all your territory, and none of the meat which you sacrificed the evening of the first day shall remain overnight until morning.

He told them another parable, “The kingdom of heaven is like leaven, which a woman took and worked into three measures of flour until all of it was leavened.”

Jesus said to them, “Watch out and be on your guard against the leaven of the Pharisees and Sadducees.”

How is it that you fail to understand that I was not talking to you about bread? But beware of the leaven of the Pharisees and Sadducees.”

Then they understood that He did not tell them to beware of the leaven of bread, but of the [false] teaching of the Pharisees and Sadducees.

Jesus repeatedly ordered them, saying, “Watch out! Beware of the leaven of the Pharisees and the leaven of Herod.”

In the meantime, after so many thousands of the people had gathered that they were stepping on one another, Jesus began speaking first of all to His disciples, “Be continually on your guard against the leaven of the Pharisees [that is, their pervasive, corrupting influence and teaching], which is hypocrisy [producing self-righteousness].

It is like leaven, which a woman took and hid in three peck measures of flour until it was all leavened.”

Your boasting [over the supposed spirituality of your church] is not good [indeed, it is vulgar and inappropriate]. Do you not know that [just] a little leaven ferments the whole batch [of dough, just as a little sin corrupts a person or an entire church]?

Clean out the old leaven so that you may be a new batch, just as you are, still unleavened. For Christ our Passover Lamb has been sacrificed.

Therefore, let us celebrate the feast, not with old leaven, nor with leaven of vice and malice and wickedness, but with the unleavened bread of sincerity and [untainted] truth.

A little leaven [a slight inclination to error, or a few false teachers] leavens the whole batch [it perverts the concept of faith and misleads the church].