He told them another parable: “The kingdom of heaven is like a mustard seed, which a man took and planted in his field. Though it is the smallest of all seeds, yet when it grows, it is the largest of garden plants and becomes a tree, so that the birds come and perch in its branches.”Matthew 13:31-32
Those listening to Jesus would have understood how small a mustard seed is. But they also would have understood that a mustard seed grows into a plant no larger than a small shrub. To say that what is usually a small shrub would not only become the largest of garden plants but then would become a tree that birds can perch in was quite an imaginary leap.
Those listening to Jesus who knew their Old Testament prophets would have heard in this parable an allusion to something God said through His prophet Ezekiel. Yes, Jesus was obviously saying that the Kingdom starts small and becomes much bigger than expected. But He was saying even more than that.
Listen to how God speaks about the kingdom of Assyria through the prophet Ezekiel.
Consider Assyria, once a cedar in Lebanon,Ezekiel 31:3-9
with beautiful branches overshadowing the forest;
it towered on high, its top above the thick foliage.
The waters nourished it, deep springs made it grow tall;
their streams flowed all around its base
and sent their channels to all the trees of the field.
So it towered higher than all the trees of the field;
its boughs increased and its branches grew long,
spreading because of abundant waters.
All the birds of the sky nested in its boughs,
all the animals of the wild gave birth under its branches;
all the great nations lived in its shade.
It was majestic in beauty, with its spreading boughs,
for its roots went down to abundant waters.
The cedars in the garden of God could not rival it,
nor could the junipers equal its boughs,
nor could the plane trees compare with its branches—
no tree in the garden of God could match its beauty.
I made it beautiful with abundant branches,
the envy of all the trees of Eden in the garden of God.
Jesus was saying that the Kingdom of God will start small but will become more powerful, more majestic, more beautiful than even the great kingdoms of the world (like Assyria).
The Kingdom of God will tower higher than all the kingdoms of the world. It will become like a great cedar of Lebanon. All the nations and peoples of the earth will rest under its shade. It will be majestic in its beauty. Nothing will rival it.
Zechariah 4:10 reminds us not to despise the day of small beginnings. Things in the Kingdom of God always start small. Yet, if we are faithful, the Kingdom will grow up around us in ways that are wildly unexpected. The Kingdom grows in ways that are beyond our imagination. This is how the apostle Paul put it when he wrote to the Ephesians:
Now to him who is able to do immeasurably more than all we ask or imagine, according to his power that is at work within us, to him be glory in the church and in Christ Jesus throughout all generations, for ever and ever! Amen.Ephesians 3:20-21