I have the following question about the Gemara on 21a.
Rav Yehuda says that Emes Veyatziv is D'oraisa while Shema is not. The Gemara attempts to disprove this view from the Mishna about a Ba'al Keri. The Mishna says that the Ba'al Keri is Meharher Shma but not Emes Veyatziv. The proof against Rav Yehuda was that if Emes Veyatziv was D'oraisa, the Ba'al Keri should be Meharhar this blessing and not be Meharher Shema. The Gemara asks that since Emes is D'oraisa then one should just think it and skip Shema. The Gemara answers that Shma has two elements while Emes has only one: Shma mentions our acceptance of Hash-m's kingdom and also Yetzias Mitzryim while Emes only mentions the latter.
My question is the following: Being that one is not Meharher Emes because it only contains one element, how does that answer the question for since Emes is D'Oraisa, it should take precedence over Shema, according to Rav Yehuda, which is only D'Rabanan! Or do we say that even though Shema is only D'Rabanan, according to Rav Yehuda, it is superior because it has both elements. But that raises another question: Are we to say that the D'Rabanan (which has two elements) is superior to the D'oraisa (namely Emes). I would have thought it would be the other way around!
I look forward to your answer.
When the Gemara says that Emes v'Yatziv is d'Oraisa, it does not mean that there is a Mitzvah in the Torah to say the blessing of Emes v'Yatziv per se. Rather, it means that the contents of Emes v'Yatziv are d'Oraisa -- namely, the Mitzvah to mention Yetzi'as Mitzrayim.
When the Gemara says that Shema is d'Rabanan, it is referring to the original text of the Shema, which was comprised only of the first two paragraphs and not the third (which contains Yetzi'as Mitzrayim), as the Gemara pointed out earlier (14b). Thus, the actual requirement to say the Shema is only d'Rabanan according to Rav Yehudah.
However, when one recites the third paragraph of the Shema, one fulfills his d'Oraisa obligation to mention Yetzi'as Mitzrayim, and Emes v'Yatziv consequently becomes only d'Rabanan.
This is what the Gemara means when it says that the Mishnah requires a Ba'al Keri to be Meharher the Shema and not Emes v'Yatziv because the Shema has two elements; it fulfills the Torah obligation to mention Yetzi'as Mitzrayim, and even though Emes v'Yatziv would accomplish the same thing, the Shema has the second element of the acceptance of Hash-m's sovereignty.