The Parable of the Mustard Seed
"[Jesus] said, 'With what can we compare the kingdom of God, or what parable shall we use for it? It is like a grain of mustard seed, which, when sown on the ground, is the smallest of all the seeds on earth, 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.' "
With the various parables recorded in Mark 4 that incorporate the metaphor of growing seed, Jesus sheds light on various truths about the kingdom of God. The parable of the sower in verses 1–20 indicates that the preaching of the kingdom will not find a lasting reception in everyone who hears it; rather, only the good soil—those whom the Lord has chosen to be kingdom citizens—will receive the Word of God unto eternal life. In the parable of the growing seed (vv. 26–29), our Lord emphasizes the mysterious, unseen growth of the kingdom according to the good pleasure of God and the patient expectation of faithful servants who plant as He has ordained. Today's passage, the parable of the mustard seed, emphasizes the contrast between the humble beginnings of the Lord's kingdom and its final, consummated form (vv. 30–32).
The kingdom of God, says our Savior, is like the mustard seed, which "is smallest of all the seeds on earth" (vv. 30–31). Now, of course, we know that there are some seeds smaller than the mustard seed. In fact, in first-century Palestine, smaller seeds than mustard seeds were planted, and Christ certainly knew that. But our Lord's point in this parable is not to give us a lesson in botany. In the culture of the day, the mustard seed was often used proverbially for the smallest thing one could think of. Jesus adapts that use in this parable. His point is that the beginning of the kingdom is tiny to the point that it seems insignificant. Hardly anyone notices its start, just as almost no one pays any attention to a mustard seed.
Yet the kingdom is not to be evaluated by its humble, nearly invisible origins. For just as a mustard seed grows into the largest of garden plants, the kingdom of God finally grows to such an extent that no one can miss it (v. 32). History bears out the truth of our Savior's teaching. He started out with twelve ordinary men whom He appointed as Apostles and a handful of other followers. He lived and died in what was considered a backwater province of the Roman Empire, and He is mentioned only in passing in the secular historical sources of that time. But since the time of Christ's ministry, death, resurrection, and ascension, the kingdom of God has been steadily growing. His church is found around the globe, and it grows even in the most hostile lands. The mustard seed is well on its way to becoming the mustard plant.
Coram Deo
John Calvin comments on this parable that "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." There is no other explanation for the growth of Christ's kingdom other than that it is the work of God. The continued existence and growth of Christ's church is a powerful confirmation of His gospel.