'Leaven' in the Bible
You shall bring from your dwellings for a wave offering two [loaves of] bread {made with} two-tenths [of an ephah] of finely milled flour; they must be baked with leaven--[the] firstfruits {belonging to} Yahweh.
And leaven shall not be seen with you in any of your territory for seven days, and none of the meat that you will slaughter on the evening on the first day shall remain overnight until morning.
And Jesus said to them, "Watch out for and beware of the leaven of the Pharisees and Sadducees!"
How do you not understand that I did not speak to you about bread? But beware of the leaven of the Pharisees and Sadducees!"
Then they understood that he did not say to beware of the leaven of bread, but of the teaching of the Pharisees and Sadducees.
And he ordered them, saying, "Watch out! Beware of the leaven of the Pharisees and the leaven of Herod!"
During {this time} [when] a crowd of many thousands had gathered together, so that they were trampling one another, he began to say to his disciples first, "Beware for yourselves of the leaven of the Pharisees, which is hypocrisy.
Your boasting [is] not good. Do you not know that a little leaven leavens the whole batch of dough?
Clean out the old leaven in order that you may be a new batch of dough, just as you are unleavened. For Christ our Passover has been sacrificed.
So then, let us celebrate the feast, not with the old leaven or with the leaven of wickedness and sinfulness, but with the unleavened bread of sincerity and truth.