Matthew 13:31

By these parables Christ encourages his disciples not to be offended and turn back on account of the mean beginnings of the Gospel. We see how haughtily profane men despise the Gospel, and even turn it into ridicule, because the ministers by whom it is preached are men of slender reputation and of low rank; because it is not instantly received with applause by the whole world; and because the few disciples whom it does obtain are, for the most part, men of no weight or consideration, and belong to the common people. This leads weak minds to despair of its success, which they are apt to estimate from the manner of its commencement. On the contrary, the Lord opens his reign with a feeble and despicable commencement, for the express purpose, that his power may be more fully illustrated by its unexpected progress. (222)

The kingdom of God is compared to a grain of mustard, which is the smallest among the seeds, but grows to such a height that it becomes a shrub, in which the birds build their nests. It is likewise compared to leaven, which, though it may be small in amount, spreads its influence in such a manner, as to impart its bitterness to a large quantity of meal. (223) If the aspect of Christ’s kingdom be despicable in the eyes of the flesh, let us learn to raise our minds to the boundless and incalculable power of God, which at once created all things out of nothing, and every day raises up things that are not, (1 Corinthians 1:28,) in a manner which exceeds the capacity of the human senses. Let us leave to proud men their disdainful laugh, till the Lord, at an unexpected hour, shall strike them with amazement. Meanwhile, let us not despond, but rise by faith against the pride of the world, till the Lord give us that astonishing display of his power, (224) of which he speaks in this passage.

The word leaven is sometimes taken in a bad sense, as when Christ warns them to

beware of the leaven of the Pharisees and of the Sadducees,
(Matthew 16:11;)

and when Paul says, that

a little leaven leaveneth the whole lump,
(1 Corinthians 5:6.)

But here the term must be understood simply as applying to the present subject. As to the meaning of the phrase, the kingdom of God, and the kingdom of heaven, we have spoken on former occasions.