In the New Testament, "leaven" is often symbolic of corrupting influence. Jesus warned of "the leaven of the Pharisees and the Sadducees", which included their teaching and hypocrisy - cf. Mt 16:5-12; Lk 12:1. Paul wrote of the danger of how "a little leaven leavens the whole lump", as he addressed the need to withdraw from the unpenitent brother - 1Co 5:1-13. This has led some to conclude that "leaven" in the parable represents something evil. But there are several reasons why this is not likely true; There is no reason why its use elsewhere must be the same here. 1) A speaker or writer is certainly free to use a figure any way they wish, even differently in different situations. 2) To read the use of the figure as found elsewhere into this passage is a form of "eisegesis" that is, reading something into the passage not actually there. Though in this case one may not be reading their own preconceived ideas into the passage, as is commonly done. But reading the ideas of another Biblical context into this one is still a form of "eisegesis". As opposed to "exegesis", which is to read out of a passage what it actually says or means, and should be the goal of proper Bible study.
