The Rabbi taught us, "The malchut shamayim [kingdom of heaven] is like a man who casts seed upon the soil; and he goes to bed at night and gets up by day, and the seed sprouts and grows. How? He himself does not know. The soil produces crops by itself; first the blade, then the head, then the mature grain in the head. But when the crop permits, he immediately puts in the sickle, because the harvest has come."
And he said, "How shall we picture the malchut shamayim, or by what parable shall we present it? It is like a mustard seed, which, when sown upon the soil, though it is smaller than all the seeds that are upon the soil, yet when it is sown, it grows up and becomes larger than all the garden plants and forms large branches; so that THE BIRDS OF THE AIR can NEST UNDER ITS SHADE."
And again he said, "What is the malchut shamayim like, and to what shall I compare it? It is like a little bit of leaven, which a woman took and hid in three se'im of flour until it became completely leavened."
This is the teaching of the Rabbi.