The importance of understanding causality is the first step in one’s salvation, and of the world. The law of cause and effect states that good thoughts and actions bring forth joy, and evil (arrogance, greed, and self love) thoughts and actions bring forth suffering in the future. The following is from the Osashizu:

About what is called “causality,” even if you desire something to happen, it may not happen. Again, even if you desire something not to happen, it may happen. This is causality, causality in the world. You have to go through your causality one way or another….. I speak of causality. To maintain tanno (positive acceptance) through whatever difficulty is the way to repent the causality from your previous actions. There is no way to repent the causality from you previous actions but this. March 23, 1899

It is important to understand causality because it allows us to understand and accept the mysteries of our daily occurrences. But more important, it allows us to plant the good seeds (good thoughts and actions) that will blossom into a joyous life in the future. Causality allows us to have control of our future.