When Deuteronomy 6:6 commands that "these words" should be displayed, remembered, and obeyed, is the phrase referring to the Shema, or is "these words" referring to the whole book? Deuteronomy 11:18-20 uses very similar language, but without using the exact wording of the Shema. Without discrediting that the Shema is the beautiful sum of the Torah to be in our minds and displayed always, could Deuteronomy 6:6-9 be commanding that not only the Shema but also the whole instruction be put on display everywhere, remembered, and obeyed?
"These words" are to be understood in a more general application.
The Chizkuni builds on this Sifrei:
והיו הדברים האלה, “and these words...shall remain” - Seeing that Moses had said previously that we should love G-d, and he had not added any adjective describing the kind of love he had in mind, he adds additional dimensions, primarily the fact that this should be a steadfast, constant feeling of love for Him. If it is, we will doubtless get to know Him better. (Sifri)
@TomW has already noted the Ibn Ezra that is to be understood more widely as a reference to all the commandments.
The Malbim explains that one should let no thought arise in their heart except for the love of G-d as if it is written on the tablet of your heart forever.
Rabbeinu Bachya would seemingly appear to demonstrate that it is an alludes to two things:
והיו הדברים האלה, “these things (concepts) shall be” - The idea of G-d’s Unity, the love for Him which Moses mentioned, shall all be deeply engraved on your heart.
Alternatively, Moses refers to the commandments, all of which should be firmly engraved on our hearts. אשר אנכי מצוך היום, “which I command to you this day, etc.” Sifri Vaetchanan 93 explains the reason that Moses adds the word היום, this day, as if he were commanding all the commandments on that day for the first time, to mean that the commandments should forever be something fresh in our minds. We should not relate to them as something deja vu, something which has lost its freshness and therefore its appeal. It should always be like some new decree the depth of which we have not yet explored. You should view them as if you had received them from Mount Sinai only this day.
Finally, Ralbag explains its application in a more general sense but does link it to the points mentioned in Shema (namely Tefillin and Mezuzah). In other words that "these word" should always be in our hearts and thoughts so we don't forget them as they are fundamental to the Torah. And that it is why afterwards (in the Shema) it goes on to detail the commandments to speak it (the Torah) out and to write tefillin and mezuzos. That is why it specifically writes "These words" to demonstrate that one should not change the order of these things nor the language and all of that is included in the term "These words".