Cyril of Alexandria
Catena Aurea · Lukasevangelium 13
Then said he, Unto what is the kingdom of God like? and whereunto shall I resemble it? It is like a grain of mustard seed, which a man took, and cast into his garden; and it grew, and waxed a great tree; and the fowls of the air lodged in the branches of it. And again he said, Whereunto shall I liken the kingdom of God? It is like leaven, which a woman took and hid in three measures of meal, till the whole was leavened.
Or else; The kingdom of God is the Gospel, through which we gain the power of reigning with Christ. As then the mustard seed is surpassed in size by the seeds of other herbs, yet so increases as to become the shelter of many birds; so also the life-giving doctrine was at first in the possession only of a few, but afterwards spread itself abroad.