Lk 13:18-21
18[Jesus] said, “What is the kingdom of God like? To what can I compare it? 19It is like a mustard seed that a person took and planted in the garden. When it was fully grown, it became a large bush and ‘the birds of the sky dwelt in its branches.’ ”
20Again he said, “To what shall I compare the kingdom of God? 21It is like yeast that a woman took and mixed [in] with three measures of wheat flour until the whole batch of dough was leavened.”
LIKE A MUSTARD SEED: “Mustard” (Greek sinapi) is a sizable annual plant with dark green leaves and yellow flowers. It has very small seeds, no bigger than the head of the pin. It can grow fast into a large bush, but it does not grow to tree size. The picture of birds dwelling in its branches is a hyperbole to emphasize a point.
The parable of the mustard seed—like that of the yeast—pictures the kingdom of God which, despite its insignificant beginnings in the person and ministry of Jesus, will eventually expand to all peoples of the earth, symbolized by the birds of the sky. Jesus’ original audience would probably have been shocked at the association of God’s reign with the tiniest of seed. They expected God’s kingdom to be inaugurated in a dramatic, earthshaking manner. Yet, as the tiny mustard seed can grow into a large shrub, Jesus’ humble ministry and the small community that he gathers around himself will surely grow into something magnificent that will embrace and shelter human beings.
This parable is an encouragement to the community of Luke and to believers of all times: the kingdom is moving towards its glorious manifestation.