The Kingdom of God.
I. Look first at the external progress of the kingdom as illustrated by the growth of the mustard seed. It is ever important to remember that Christianity, at first like a small grain of seed, spread throughout the world, until the nations of the earth came to flock like birds to its protecting shelter, by no aid except its own inherent spiritual power. There was nothing to help it in the character of its early teachers. There was nothing to make its progress easy in the conditions of the Jewish and Gentile worlds. People say sometimes that they find it hard to believe the miracles on which Christianity is based surely the grandest, greatest miracle is the existence of Christianity itself. If, then, there was nothing in the outside world to which it appealed, nothing in the natural hearts of men which it came to satisfy, how are we to account for the spread of Christ's kingdom except by attributing to it some spiritual power of its own? Does not the second parable, that of the leaven, come in here to explain to us the secret of those earlier teachers' spiritual power? The grain of leaven, put into their hearts, when first the Master called them, gradually permeated and transfused their entire nature. The whole man was leavened. The early teachers of Christianity used to describe this leaven by the word "faith." To us faith has become too much merely the cry of a party, the shibboleth of a sect. To an apostle it meant everything. It meant an intensely personal love for Christ. It meant the entire absorption of all the heart's deepest feelings in devotion to Him. This it was this burning love flaming in their hearts, this principle of enthusiasm transforming their lives which made these weak men strong. The outward kingdom grew and increased, because the invisible kingdom so wrought in the hearts of disciples that their whole nature was leavened by it.
T. T. Shore, Some Difficulties of Belief,p. 189.
References: Matthew 13:31-33. Christian World Pulpit,vol. v., p. 167. Matthew 13:32; Matthew 13:33. H. W. Beecher, Ibid.,vol. xxix., p. 73.