Another parable He spoke to them: "The kingdom of heaven is like leaven, which a woman took and hid in three measures of meal till it was all leavened." (Matthew 13:33)
I have heard (and read) expositions on this parable of Jesus in which the expositor proposes that it teaches that the Kingdom is as leaven to the world and that the world will ultimately be permeated with the goodness of the Kingdom.
This is in diametric opposition to the use of the term and the symbolism of leaven in the scriptures. From the earliest recordings through the teachings of Christ, and those of Paul, leaven invariably has been representative of evil.
In that light, therefore, Jesus is teaching us that the kingdom of heaven is subject to this danger: evil concepts or error introduced and mixed in will ultimately permeate the entire church, given the right conditions.
What are those conditions? Anyone who has ever attempted to bake a loaf of bread or prepare yeast rolls for a major dinner knows that the introduction of the leaven is a critically important step, but that it will not accomplish the mission of permeating every portion of the dough unless the conditions are right. The temperature of the dough must be exactly right! And what is that temperature? It must be lukewarm!
If the dough is set in a cold environment, say the refrigerator, the yeast will not work. If it is heated to "hot" it will not work. A lukewarm environment is the only one in which the leaven will permeate the dough.
This fact sheds light on God's warning: “I know your works: you are neither cold nor hot. Would that you were either cold or hot! So, because you are lukewarm, and neither hot nor cold, I will spit you out of my mouth." (Revelation 3:15, 16)
Consider also that the parable says the woman hid the leaven in the flour. I think it is not the mission of Christ's disciples to hide the Gospel in the world.
Scripture further teaches me to "Study to show yourself approved unto God, a workman that need not to be ashamed, rightly dividing the word of truth." (II Timothy 2:15)
This short story of Jesus is an excellent example of the necessity of "getting it right."