The Harirai Kedem continues by saying that there may be a significant halachic ramification based on this explanation. The Shulchan Aruch (Orach Chaim 268:4) rules that if one davens the weekday Shemoneh Esrei on Shabbos or Yom Tov and only mentions Shabbos or Yom Tov somewhere in his Shemoneh Esrei (even though he did not mention it in a separate berachah) he has fulfilled his obligation. Perhaps on Rosh Hashanah one would not have fulfilled his obligation in this manner. Since the obligation to mention the day of Rosh Hashanah is derived from a new halacha, perhaps it must be mentioned in a separate berachah (at least by Mussaf).
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