This Sunday is the last time the text is from Matthew 13. Jesus has seven parables within this chapter--a nice, biblical number. And I think it is unfortunate that the middle parable, the fourth one, has been overlooked in the lectionary.
Admittedly it is quite small and is also introduced in a very normal fashion. When Jesus is giving the crowd the parable of the weeds, the text says that he 'put another parable before them....' The text says the very same thing regarding the parable of the mustard seed. But when it comes to the parable of the leaven, the text just says that he spoke to them another parable (13:24, 31, 33). Perhaps, with this normal introduction, it has some greater significance.
Leaven (or yeast) is an amazing thing. It works its way into all the bread. I think it is interesting that the text says the woman 'hid' it in the flour. And that word and idea appears elsewhere in this chapter.
There is a treasure that is hidden in a field. There is a man who FINDS a pearl of great value. Jesus, at the end of all these parables, says that 'every scribe who has been trained for the kingdom of heaven is like a master of a house, who brings out of his treasure what is new and what is old (13:52).' Something brought out of the treasury has been previously hidden from sight.
That God's kingdom is a hidden one, now THAT is significant. God could make his kingdom quite obvious--he is God! But he has chosen a different way in which to work. He is choosing to be known in a different way.
If one would allow a connection between the five sermons in the Gospel according to Matthew and the five books of the Pentateuch, this sermon in Matthew 13, the middle one, would be connected to Leviticus, the middle book. And Leviticus has a way of being overlooked in the Old Testament.
There are lots of rules and guidelines--wear this, kill that. But all through the book God is dishing out his holiness, and he is dishing it out in a very hidden way.
This God is not like the others. God chooses to be stay with his chosen people while they were wandering around in the wilderness. He chooses to give out forgiveness when an innocent lamb is killed. When blood has been shed, God says that sins have been forgiven. He chooses to remain, for the most part, hidden, so he can be known for his love, not his power.
I am hoping you see a theme here.