He said therefore, “What is the kingdom of God like? And to what shall I compare it? It is like a grain of mustard seed that a man took and sowed in his garden, and it grew and became a tree, and the birds of the air made nests in its branches.”
One of the glories of Jesus’ parables is that they are written on multiple levels. You do not need to be an expert to understand them; Jesus knew the human ability to apprehend apprehend truth through story (the emphasis on narrative is one of the few things that post-modernism gets right).
This parable is no exception. On the surface, it teaches that the kingdom starts out small and apparently insignificant, but soon grows from a humble beginning to become great. This is certainly true of Christianity, which in a few hundred years spread from one executed Jewish carpenter throughout the Roman empire. And it is true as well of those who choose to live in the Kingdom and let it change them. But why compare the Kingdom of God to a tree? And what do birds have to do with it?
If you’re familiar with the right portions of the Old Testament, these questions resolve themselves and give a surprising depth to this short parable. Compare it, firstly, to Nebuchadnezzar’s dream in Daniel 4:
10 The visions of my head as I lay in bed were these: I saw, and behold, a tree in the midst of the earth, and its height was great. 11 The tree grew and became strong, and its top reached to heaven, and it was visible to the end of the whole earth. 12 Its leaves were beautiful and its fruit abundant, and in it was food for all. The beasts of the field found shade under it, and the birds of the heavens lived in its branches, and all flesh was fed from it.
Daniel interprets the tree as Nebuchadnezzar himself (4:20-22) and, by extension, his kingdom. The details in Nebuchadnezzar’s dream explain why a tree is such a good metaphor for a kingdom: it provides food, shelter, and safety to the animals (kingdom subjects), who are drawn to it.
Let’s incorporate this into our understanding of Jesus’ parable. The kingdom begins tiny and seemingly insignificant, but when it is grown it provides safety and protection and sustenance to those who live in it. The kingdom promise of safety and protection goes out to all who seek shelter.
It may be stretching things, but I think I hear an echo of Jesus’ sacrifice in the parable. Jesus, in hanging upon a tree, draws all men to himself (John 12:32) and feeds them with His body and blood. In other words, his death accomplishes what the kingdom mustard-tree symbolizes.
An even clearer Old Testament echo is found in Ezekiel 17. For complete context you really need to read the whole chapter, but the most relevant portion is at the end:
22 Thus says the Lord God: “I myself will take a sprig from the lofty top of the cedar and will set it out. I will break off from the topmost of its young twigs a tender one, and I myself will plant it on a high and lofty mountain. 23 On the mountain height of Israel will I plant it, that it may bear branches and produce fruit and become a noble cedar. And under it will dwell every kind of bird; in the shade of its branches birds of every sort will nest. 24 And all the trees of the field shall know that I am the Lord; I bring low the high tree, and make high the low tree, dry up the green tree, and make the dry tree flourish. I am the Lord; I have spoken, and I will do it.”
This is a promise that God will restore Israel. He will take a small, tender twig and plant it, water it, care for it. It may not look like much to begin with, but God will make Himself known through it. He will “make high the low tree”. The birds figure prominently in the metaphor, and the tree’s shade serves to emphasize the protection and rest that it offers.
It seems certain to me that Jesus had this passage in mind. With this background, we can say a few more things about the parable. Jesus is declaring that the Kingdom of God which he preaches will bring the restoration of Israel promised by the prophets. Also, God is watching over and tending the growth of the Kingdom-tree. He intends to display his glory through it, to show how superior this tree is, which at first seemed insignificant, to all other trees, all other kingdoms. God brings low the high tree, dries up the green tree, but this tree alone has been chosen and will stand forever. Come, all you who are weary and heavy-laden, and find rest in its shade.