Parable of the leaven

Matt 13:33a Another parable spake he unto them; Luke 13:20 And again he said, Whereunto shall I liken the kingdom of God?
Matt 13:33b The kingdom of heaven is like unto leaven, which a woman took, and hid in three measures of meal, till the whole was leavened. Luke 13:21 It is like leaven, which a woman took and hid in three measures of meal, till the whole was leavened.

Matt 13:34 All these things spake Jesus unto the multitude in parables; and without a parable spake he not unto them: 35 That it might be fulfilled which was spoken by the prophet [1], saying, I will open my mouth in parables; I will utter things which have been kept secret from the foundation of the world.

[1]Psalms 78:2 I will open my mouth in a parable: I will utter dark sayings of old. This is from the opening of a speech detailing God's deeds and the people's lack of faith.