Recently I've been devotionally using Terry Johnson's helpful book, The Parables of Jesus.
One of the things that I've been taught as I've studied these parables is to be careful to look at the context into which they are spoken. They were never spoken into a vacuum. Sometimes the immediate context is given; other times, one needs to work it out.
This has made me think about the context into which Jesus speaks the parables of Matthew 13 (and their equivalents in Mark 4 and Luke 8). I'd never really thought about the context of these parables. But now I think they are addressing false ideas of the Messiah and the kingdom that were about in the 1st Century.
The disciples expected the kingdom to come through a military victory; Jesus says that the kingdom comes through responding rightly to the word of God. The disciples expected the kingdom to inaugurate a radical new era; Jesus says that the kingdom really has come but will coexist with evil until judgement comes. The disciples expected the kingdom to be irrepressible; Jesus says that the kingdom will be opposed but will grow anyway. The disciples expected the kingdom to arrive with fanfare and victory; Jesus says that the kingdom has tiny beginnings and is established, miraclously but normally through gradual growth. The disciples expected to experience immediate victory in the kingdom; Jesus says that it will require sacrifice - but that it is worth infinitely more than the cost of discipleship. Indeed, entering the kingdom is worth it - whatever the cost.
These lessons of the kingdom were instructive not only for the disciples, but also for us. I've been particularly encouraged by the way in which Jesus says that the kingdom grows. It's true that the kingdom sometimes grows spectacularly - but more often it grows slowly and gradually as individuals accept Jesus' Lordship over their lives.