To what shall we compare the Kingdom of God? "The Kingdom of God" is a concept that was not alien to the ears of those who were listening to Jesus. The sons and daughters of Israel who constituted the larger portion of Jesus’ audience understood themselves as belonging to the kingdom of God. To them, their nation (land) and the kingdom of God were synonymous. Had the Lord not chosen them from among the nations? Had the Lord not made Israel God's first born? It was a privilege that they took pride in. In Jesus’ many parables about the kingdom of God, his main objective was not to dispute this understanding. He only intended to give it a new interpretation that was commensurate with their time. 
Because of the foregoing understanding, because of being "born into" it, the kingdom as a concept remained very passive and inert thing. It must have even been taken for granted by those who took pride in it. One did not have to struggle or do anything to belong to the kingdom. Because belonging to the kingdom, as it were, was assured, the people lost interest in what the kingdom was about. This is why when Jesus emerged into the scene, he preached the in-breaking of the kingdom, that is, the coming alive of the kingdom. The parables that he uses in today’s reading to describe the kingdom portrays a kingdom that is engaged, a kingdom that is active. Just as a seed that is planted must grow because of coming into contact with the moist soil, so is the seed of the kingdom planted in men’s hearts. The kingdom must grow inside of men and women, and that growth must be felt by others. For it is only when the effect of the kingdom engaging those belonging to it that the kingdom can be said to be growing.