Parable of the Seed

And He was saying, "The kingdom of God 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."

Mark 4:26-29 (New American Standard Bible)