The Talmud discusses when a person can say Shema in the evening. It's connected to the words in Deuteronomy to remember the commandments when you're lying down and getting up. I can see the connection. I can also see how this helps both individuals and the community to remember and fulfil the commandment. I also understand why it's good to follow the community in such matters.
What I don't get is the stretch from simply saying it whenever you go to bed, to this whole concern of deciding what time is appropriate to do so every day. The Gemara asks why the question 'from what time' was brought, but the answer isn't given on the level that I'm wondering about.
Is this interest in times a 'fence' measure, to make sure an original (oral) Torah law to say Shema is kept? (Similarly to the statement in the mishnah about why the sages said 'until midnight'.) Or perhaps the practice of saying Shema itself emerged not from a Torah law per se. Perhaps the Sages wanted to create a tradition that would help us remember the things Deuteronomy discusses; and then times were also given. Or do you think that Shema was said at particular times from the days of Moses, and that the Mishnah here was recording something original to the oral Torah?
I'd value hearing more about how rabbinic tradition handles such things, to come to the decisions you have before you today, with reference to this particular question. In this case, what is the connection between what is written in the verses and what is passed down through the generations? Is it even possible for us to know why it matters to specify times for saying it?
Edit
I'm not challenging the validity of the Talmud or the binding nature of practice about this point, within the context of Judaism. I'm just wondering if there's anything else in rabbinic writings about how the Shema came to be said in this way. Or, if it did happen to be a case of rabbinic tradition and fences: How might it hypothetically have happened within the processes of Jewish law?