"The kingdom of heaven is like a grain of mustard seed, which a man took and sowed in his field . . . . the smallest of all seeds, but which when it grows up . . . becomes a tree" (Matthew xiii: 31).
We find our Lord again speaking in parables; little stories about things familiar to His listeners to help them understand and remember important points of doctrine. To understand the point He is making, we need to know a little about mustard seeds and the way the Jewish people went about baking their bread.
In biblical times, people baked their own bread from flour that they ground themselves. In order to make that bread rise they had to have yeast, and in those days they could not jut run out to the grocery store to buy a little yellow packet of Fleishman's. A Jewish household cultured its own strain of yeast by continually keeping a mass of raw dough a crock in a darkened corner of their house. When they made a new batch of dough, they mixed in a bit from the old batch, and the yeast in it grew within the new. There were, quite literally generations upon generations of yeast cultures in the Jewish bread. (They did the same thing, by the way, with grape juice and milk to make wine and cheese or yogurt.)
So, our Lord here is describing a sort of immortality, and certainly describing a process of great power and potency. The yeast goes on, seemingly forever. And only a little bit is required to leaven the large new mass of dough. The little bit of fermented dough permeates every part of the new dough, making it, as it were, alive with the process of fermentation.
And He is alluding to something similar with the grain of mustard seed. For these seeds, which are about the size of poppy seeds -- the little black ones, that you get on the seeded roles -- yet they grow into a plant literally the size of a tree. A plant large enough for the birds to roost, having pretty flowers, and a strong, savory, flavor in its greens. Here again, He is describing something of power and potency, and something seeming to come alive from a speck of dried out material.
Our Lord described these to phenomena, very common to His Jewish audience, and told them that they were symbolic of the kingdom of heaven -- that somehow God would work in them in the same manner as the leaven worked in dough; in the same manner as the tiny speck growing into a tree.
And, not only would He work in them, but they, in turn, would work in the same way on the people around them. So that God would take a handful of individuals, like so many mustard seeds, and grow them into His Church. So that He would take just a pinch of leaven, and ferment entire communities, and whole societies with the life of divine grace. So that the Mystical Body of Christ, like the generations of yeast, would have an immortality of its own; going on forever until the end of time.
Quite likely, if they hadn't received assurances like this from our Lord, the apostles would have been doomed to failure in their mission. How could 12 sane men set out to change the world, unless they had been given this kind of assurance that their task was at least possible -- and in fact guaranteed by the one who makes all of the seeds to sprout, and the birds of the air to roost in them?
If we have doubts about our own mission here -- a small group, huddled in a small room -- we should take comfort from these parables, and from what we have seen the Apostles do. All we have to do is Christianize a small piece of southern Florida -- God isn't asking us to change the world! But, at least in principle, He is giving us power strong enough to do so.
He is first of all, offering us His own personal love -- the power behind all creation. And, He is asking nothing more than that we return that love. He is asking no more than that we should spend a few quiet moments now and then, looking down into our own souls ... Looking down into our own souls, and finding Him there. And, on finding Him, that we should spend a few moments sharing His love.
He is asking us to do good, and to keep His Commandments -- not because the Church tells us to, or our parents, or our children; not because it is good for society or for our own well-being; not even because it is the rational, human thing to do -- He is asking us to do good and keep His Commandments because we have looked into the depths of our own being, and found Him there within ourselves. He is asking us to keep the Commandments because we love Him,
He is asking us regularly to unite with Him in His Sacraments -- not just because this is a respectable thing to do, or that it makes all of the same kind of sense that keeping the Commandments makes -- but because we have looked within ourselves, and have been drawn by His holiness and His desire for us; so that we don't ever want to abandon Him to dwelling in the tabernacle in the loneliness of an empty church.
The kingdom of heaven is like a mustard seed; the kingdom of heaven is like leaven. It is filled with immortality; it is filled with great power and potency. Immortality, power, and potency, which come to us directly from the life and love of God dwelling in our souls -- if only we let Him; and if only we look into our souls to find Him.