שם שם לו חק ומשפט

Often, מדרש אגדה is meant to highlight an idea that is "between the lines" of the Biblical text itself.

We are told (מכילתא, brought in :סנהדרין נו) that three sets of commandments were given at מרה:

1. דינים
   
   
2. שבת
   
   
3. כיבוד אב ואם*
   
   * It's been suggested the version of רש"י in חומש is due to a copyist mistaking the abbreviation כ"א (i.e. כיבוד אב) for פ"א (i.e. פרה אדומה).

Perhaps the underlying concepts of all three of these sets of laws can be learned from the story that happened at מרה.

1. It was wrong for בני ישראל to rush to judgement of משה and God based on an initial observation (the lack of water). The "other side" had to be allowed the chance to present its case. This is the lesson of דינים.
   
   
2. Everything that God does for us, even miracles, is built into the Creation. A "natural" solution like throwing a tree into the water is possible because God provided for everything when he created the world. This is the lesson of שבת.
   
   
3. When בני ישראל were helpless on their own, God ("אבינו שבשמים") provided for them. In gratitude for this care, we owe Him our respect. This is the lesson of כיבוד אב ואם.