Matthew 13: 31 - 35
31 Another parable he put before them, saying, "The kingdom of heaven is like a grain of mustard seed which a man took and sowed in his field;
32 it is the smallest of all seeds, but when it has grown it is the greatest of shrubs and becomes a tree, so that the birds of the air come and make nests in its branches."
33 He told them another parable. "The kingdom of heaven is like leaven which a woman took and hid in three measures of flour, till it was all leavened."
34 All this Jesus said to the crowds in parables; indeed he said nothing to them without a parable.
35 This was to fulfil what was spoken by the prophet: "I will open my mouth in parables, I will utter what has been hidden since the foundation of the world."

EWTN