“A little leaven leavens the whole loaf.”
Keep in mind that when this parable was first told people did not understand how yeast worked. They only knew the effects of the yeast when put into a batch of dough. It would change the whole batch no matter how big that batch was.
This is true about our spirituality no matter what that spirituality is. What we really deep down feel to be true affects us in many ways. What we believe – not the nice objective statements of dogma that make up so many creeds, but the visceral indescribable perceptions (the kind of things that you pay big money to a psychiatrist to help you discover within your subconscious) – controls mental and physical health in many ways.
Ancient systems of thought like charkas developed this idea in detailed ways. Physical pains do not always have physical causes. When we cannot cope with an emotional pain we displace that pain somewhere in our bodies.
If pain is not caused by genetics, diseases or some external force like accidents or disasters, then we need to look at our spirituality. Using the imagery of yeast that is found in other places in our ancient texts, “throw out the old yeast and take in the new”.
But it is not only our physical bodies that our spiritual yeast effects. Part of the treatment for addiction includes spiritual work. The 12 Step programs used in many treatment programs are basically spiritual in nature. Our emotional well-being starts with a healthy spiritual yeast.
Relationships also are affected by the spiritual yeast within us. If we are quick to condemn others we reveal a judgmental (not just a discerning) spirit. If we are afraid to establish or commit to relationships we may be revealing that a spirit of fear controls us.
The parable of the yeast makes a simple statement of common knowledge. The use we make of this parable as a metaphor is up to us.