May I please ask you a question ?
I am already a zaken (between 60 and 70), and I have never received a satisfactory answer to the following questions.
Where is the source of the mitzvah de’oraisah of krias Shemah ?
The Torah refers to “hadevarim ha’eileh”, a noun. Then the next posuk uses pronouns; “ve’shinantam” and “ve’deebartah bam”. It seems that “ve’shinantam” refers to Torah (hence, “hadevarim ha’eileh” is divrei Torah in general). It would seem that the next phrase in the same posuk, using a pronoun, should also be referring to divrei Torah in general. So where is the mitzvah of krias shemah ?
If we find where the Torah does enjoin us to recite shemah, perhaps it just refers to the statement “shemah Yisrael”. Where is the mitzvah to include the commanding pesukim, ie. “ve’deebarta”, “u’kshartam”, “u’chsavtam” ?
The simple meaning of “Hadevari Hoele” is referring to these words, meaning the first parsha of kriyas shema, and on that it says that it is to be read uvshachbecha, uvkomecha”, when you wake up and go to sleep. The same applies to the second part of kriyas shema. Chazal saw from this that the parsha of shema should be read in the daytime and at night. In Brachos 11a, the Mishan discusses a dispute between Beis Shammai and Beis Hillel, regarding the exact body position that one should have while saying this paragraph. It is clear that they understood that these words are referring to the reading of this portion. See R’ Hirsh Devorim 6 verses 6 and 7.
Regarding what is included in the mitzva, the commentaries talk about it, but R’ Nirsh discusses this as well.