Amazing Dvar Torah For Parshas Bo

פרשת השבוע, בא מאת אבי מורי ר' צבי יודא פרידמן זלל"ה   Shmos 12- 39. ויאפו את הבצק – עוגות מצות Rashi explains:  "בצק שלא החמיץ קרוי מצה" (unleavened dough is called Matzoh)   One of the כללים (rules) in Rashi is that he explains   the word the first time, it appears in the Torah or Gemoro. Why did Rashi wait until pasuk # 39 to explain what matzah is?   The word matzah appears in  Breishis 19 – 3   ומצות אפו ויאכלו. It also appears in this Parsha three times before this Pasuk (12-39)    1)Shmos 12- 17    ושמרתם את המצות--   2) 12 -18    בערב תאכלו מצות 3) 12- 20.בכל מושבותכם תאכלו מצות     Why did Rashi not explain what a Matzah is in Bereishis or at least the first time in this Parsha? Answer: The Gemoro יומא ע"ה says: By the מן (Manna) it is written,  וטחנו- עוגות- לחם, לחם (bread) was for  צדיקים,  וטחנו (needed grinding) for רשעים עוגות was for the בינונים. Rashi explains the word עוגות," משמע קודם אפיה" עוגות is before it is baked. The בינונים didn’t need to grind the מן but they still had to bake it. Accordingly here too when it says עוגות מצות It means unbaked Matzoh dough. There is no need for Rashi  to explain what a baked Matzah is. Every child knows that unleavened baked bread is called "Matzah". In Pasuk 12 – 39 where it says for the first & only time עוגות מצות, which means unbaked Matzos Rashi needs to explain that not only is an unleavened baked bread  called Matzah, but also unleavened dough is called  Matzah.