Kingdom Theology in a Nutshell

Mark 4:30 And he said, “With what can we compare the kingdom of God, or what parable shall we use for it? 31 It is like a grain of mustard seed, which, when sown on the ground, is the smallest of all the seeds on earth, 32 yet when it is sown it grows up and becomes larger than all the garden plants and puts out large branches, so that the birds of the air can make nests in its shade.” 33 With many such parables he spoke the word to them, as they were able to hear it. 34 He did not speak to them without a parable, but privately to his own disciples he explained everything.
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It is interesting that birds and squirrels play a part in the distribution of seeds across the earth. Some seeds even have to be eaten and digested before they can germinate. There's quite a bit of symbolism there, but the image I'd like to zoom in on is of the mustard seed - let's call it an acorn instead. Set aside for a moment the obvious truth that the Kingdom of God is something we like to call heaven. What does Jesus mean when he says that His Kingdom is like an acorn, starting so small and growing so big? Why is it important for him to preach this message? Why doesn't he just focus on the same message that John the Baptist preached - 'repent'? Why does he insist on describing it to them? Is this functional knowledge or just a nice-to-know-fact? This last question is key because for many of us, its easier to think of God's Kingdom as though it were a country club - you're either in or you are out. But here God is talking about His Kingdom as though it were a living thing in an of itself - something which starts small, has roots in the earth, grows large into the heavens and provides shelter for all kinds of creatures. This image of the Kingdom is a bit strange, as though Heaven itself might have roots planted in our current reality. And this is exactly what Jesus is preaching. He comes from the root of Jesse, and lineage of David, but Jesus is the Root from which the Kingdom grows, or perhaps the acorn, to follow our analogy. He is the vine and we are the branches . He is the tree who provides our shelter and our way to transcend the world, but his roots in the world allow him to remain connected with us.The Kingdom of God here and now is like an acorn which has taken root and grown into a strong young tree, but there is much more growing to do. This is functional knowledge because in knowing the Kingdom of God is rooted in our midst and growing into full fruition, we can't sit idly by and wait. We must participate in the growing. We cannot force it to grow the way we would like or at the speed that we would like, but we can certainly be productive by doing the types of things Jesus did - loving the outcast, healing the sick, speaking the truth in love... His Kingdom advances when we invite people into the promise of a heavenly afterlife, but also into the promise of heaven taking root in the earth here and now. The already and the not yet - the Kingdom is coming and the Kingdom is at hand.