Moses worries. He worries that one day in the future the Israelites might forget what they witnessed at Mt. Sinai and, being led astray by their baser desires, ignore the Torah they were given (Deuteronomy 4:9). So Moses stresses that they must inform their children and grandchildren about the revelatory even at Sinai when they “stood before God at Horeb” (4:9–10). (Horeb is a geographical synonym for Sinai.)
Nahmanides, though, has a different problem. The wording of Moses’ warning puzzles Nahmanides. Why does Moses tell the people to remember standing before God at Sinai and not the words that Moses himself spoke in the name of God at Sinai? It would seem that the latter wording better relates to the fear expressed by Moses that the people would forget the content of the Torah more than the event of the giving of the Torah.
Like any proficient commentator, Nahmanides would not ask this question unless he already had an answer. His answer is that all conduct that is based only on human opinion (what legal theorists refer to as positive law) can be altered by later human opinions. Were Moses to have said ‘Remember what I told you at Sinai’ the people could very well have reasoned that was Moses’ opinion. However, should another leader arise with a variant opinion – a contradictory opinion – we would follow it. But conduct based on a singular, supernatural event could not be altered. Any attempt to divert the people from following the content of the Torah belies its reliability. The people experienced the unique event at Sinai when God appeared to them directly. The event itself is what validates the message, not the rhetoric of the messenger.
Nahmanides, like many moderns, struggled with the profound question of the authoritativeness of an ancient tradition. To be sure, Nahmanides fully accepted the Rabbinic tradition that qualifies and modifies the scriptural tradition. He is most certainly not a Karaite (i.e. that sect of Jews who largely rejected Rabbinic interpretation of Torah). Nonetheless, he steadfastly maintained that the essential elements of Judaism are inalterable and it is that foundational belief he propounds.