Question: I was wondering why the Mishna lists specifically these three mitzvos that he is "putor" from. Tosafos on the spot explains why he is putor from kreias shma but that is it. The Maadanei Yom tov brings Tosafos on daf 14b that says because shma is because it has a set time. Ok, that explains shma, but what about tefilla and tefillin which can be done theoretically all day? And R'Yonah says since these three are so strict and he is putor, certainly the rest of the mitzvos are also putor, so why did the mishna have to include tefilla, why is tefilla so "chumor", it should have been enough to include shma to include mitzvos that have a set time and to include tefillin to teach you all the other mitzvos?
Thank you very much for taking out time to answer my question. I really appreciate it.
The Mishnah may have included Tefilah because one is able to fulfill his obligation by saying just a few short words of prayer to Hash-m. We might have thought, therefore, that he is not exempt from Tefilah, and that is why the Mishnah must teach us that he is indeed exempt.
Alternatively, these three Mitzvos are "Chamurim" because they all express the concept of accepting upon oneself Hash-m's dominion: Kri'as Shema, as the words themselves declare; Tefilah, for one acknowledges that Hash-m is in control of everything; and Tefilin, as the Gemara earlier in Berachos said (6a) that "the name of Hash-m is called upon you" when wearing Tefilin.
See also the other commentators on the Mishnah.