In an agrarian society, weather influenced economics. Crops depended on rain, so the people became experts in reading the sky and forecasting weather because their financial welfare was at stake. We are very much like that. We are often more interested in the trends of the stock market or who the 49'ers are going to pick than we are in seeking God's perspective and wisdom. The next scene opens with Jesus and his disciples sitting in a boat crossing the sea of Galilee.
Yeast is used in the Bible as an illustration of the invisible power of sin.
Just as yeast permeates dough and changes its characteristics, so does sin infect our lives. Thus Jesus warned his followers to be alert and attentive to this dangerous spiritual reality. The first soil never produced anything because the seed was taken away. The second soil was rocky ground and the seed quickly withered under the heat of the sun. The fourth soil produced a crop of great bounty.