The essay describes how leaven was perceived during Israelite times. In what ways it came to be incorporated into the theology of the Hebrew Bible. The inheritance the leaven carries with it is used in various ways in Nt. The essay describes Paul's and Jesus' use of leaven and gives a context for why this use was reasonable. The essay theorizes that the knowledge that the leaven came from Egypt meant that it could not be incorporated into the Israelite cult without exception. Egypt is in some respects the image of idolatry because several gods are worshipped. This means that the sourdough gets a legacy that needs to be managed. The bread leavened with sourdough is necessary during a time when there is a shortage of food at certain times. A bread leavened with sourdough provides more nutrition and makes it possible to store food for a longer period of time. The essay shows how the regulation in the Hebrew Bible lives on in Paul's letter in Nt. Jesus' references to the leaven are more general, where the leaven represents the spiritual in man. Leaven also takes on a different meaning in Nt in that it is attributed both positive and negative qualities. Leaven goes from being regulated in the Hebrew Bible to becoming in the NT a representative of the spiritual in man.