Ambrose of Milan
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. He next likens the kingdom of God to leaven, for it follows, And again he says, Whereunto shall I liken it? It is like to leaven, &c.
But we are the meal of the woman which hide the Lord Jesus in the secrets of our hearts, until the heat of heavenly wisdom penetrates our innermost recesses. And since He says it was hid in three measures, it seems fitting that we should believe the Son of God to have been hid in the Law, veiled in the Prophets, manifested in the preaching of the Gospel. Here however I am invited to proceed farther, because our Lord Himself has taught us, that the leaven is the spiritual teaching of the Church. Now the Church sanctifies with its spiritual leaven the man who is renewed in body, soul, and spirit, seeing that these three are united in a certain equal measure of desire, and there breathes forth a complete harmonyof the will. If then in this life the three measures abide in the same person until they are leavened and become one, there will be hereafter an incorruptible communion with them that love Christ.