משה רבינו לא האמינו בו ישראל מפני האותות שעשה שהמאמין על פי האותות יש בלבו דופי שאפשר שיעשה האות בלט וכשוף אלא כל האותות שעשה משה במדבר לפי הצורך עשאם לא להביא ראיה על הנבואה היה צריך להשקיע את המצריים קרע את הים והצלילן בתוכו צרכנו למזון הוריד לנו את המן צמאו בקע להן את האבן כפרו בו עדת קרח בלעה אותן הארץ וכן שאר כל האותות ובמה האמינו בו במעמד הר סיני שעינינו ראו ולא זר ואזנינו שמעו ולא אחר האש והקולות והלפידים והוא נגש אל הערפל והקול מדבר אליו ואנו שומעים משה משה לך אמור להן כך וכך וכן הוא אומר פנים בפנים דבר ה' עמכם ונאמר לא את אבותינו כרת ה' את הברית הזאת ומנין שמעמד הר סיני לבדו היא הראיה לנבואתו שהיא אמת שאין בו דופי שנאמר הנה אנכי בא אליך בעב הענן בעבור ישמע העם בדברי עמך וגם בך יאמינו לעולם מכלל שקודם דבר זה לא האמינו בו נאמנות שהיא עומדת לעולם אלא נאמנות שיש אחריה הרהור ומחשבה
The Jews did not believe in Moses, our teacher, because of the wonders that he performed. Whenever anyone's belief is based on wonders, [the commitment of] his heart has shortcomings, because it is possible to perform a wonder through magic or sorcery.
All the wonders performed by Moses in the desert were not intended to serve as proof [of the legitimacy] of his prophecy, but rather were performed for a purpose. It was necessary to drown the Egyptians, so he split the sea and sank them in it. We needed food, so he provided us with manna. We were thirsty, so he split the rock [providing us with water]. Korach's band mutinied against him, so the earth swallowed them up. The same applies to the other wonders.
What is the source of our belief in him? The [revelation] at Mount Sinai. Our eyes saw, and not a stranger's. Our ears heard, and not another's. There was fire, thunder, and lightning. He entered the thick clouds; the Voice spoke to him and we heard, "Moses, Moses, go tell them the following:...."
Thus, [Deuteronomy 5:4] relates: "Face to face, God spoke to you," and [Deuteronomy 5:3] states: "God did not make this covenant with our fathers, [but with us, who are all here alive today]."
How is it known that the [revelation] at Mount Sinai alone is proof of the truth of Moses' prophecy that leaves no shortcoming? [Exodus 19:9] states: "Behold, I will come to you in a thick cloud, so that the people will hear Me speaking to you, [so that] they will believe in you forever." It appears that before this happened, they did not believe in him with a faith that would last forever, but rather with a faith that allowed for suspicions and doubts. (Touger translation)
I am trying to figure out what the qualitative difference is between what happened at Sinai and any of the other wonders mentioned. The only things mentioned here that happened at Sinai are that "we" saw and heard thunder, lightning, Moshe entering the clouds, and a voice speaking to Moshe.
This does not appear to be qualitatively different from a regular miracle. In fact I'm not even sure it sounds quantitatively different from the other miracles. Moshe split the sea, brought food from the sky, produced water from a rock, and opened the earth. He also walked into clouds accompanied by thunder, lightning, and fire, and we heard a voice.
Rambam's point here is that miracles are not sufficient proof because one could argue that the miracles were somehow done by man himself and are not really from God. So if an onlooker would think that Moshe somehow split the sea, rained food from the sky, drew water from a rock, and split the earth on his own, why couldn't they think that he had produced the thunder, lightning, fire, and voice at Sinai on his own?
What was it about the events at Sinai that proved that it was a divine revelation and not merely another miracle?
Some people will undoubtedly answer that the difference is that at Sinai the people actually experienced the prophetic revelation as opposed to the other cases where they merely witnessed the miracles. Indeed this seems to be R. Yosef Albo's understanding of this point in Sefer HaIkkarim 1:18. However, even if we were to grant that experiencing a prophetic revelation is qualitatively different from witnessing a miracle, in that a prophet somehow knows with certainty that he is prophesying (which itself is a question), I don't think it would help us here. Rambam himself in Guide for the Perplexed explains at length that what the masses experienced at Sinai was not prophecy; indeed he writes that it is impossible for people who don't have the prerequisites of prophecy to prophesy.
Guide for the Perplexed 2:32
We hold that fools and ignorant people are unfit for this distinction. It is as impossible for any one of these to prophesy as it is for an ass or a frog; for prophecy is impossible without study and training; when these have created the possibility, then it depends on the will of God whether the possibility is to be turned into reality. (Friedlander translation)
As to the revelation on Mount Sinai, all saw the great fire, and heard the fearful thunderings, that caused such an extraordinary terror; but only those of them who were duly qualified were prophetically inspired, each one according to his capacities. Therefore it is said, "Come up unto the Lord, thou and Aaron, Nadab and Abihu." Moses rose to the highest degree of prophecy, according to the words, "And Moses alone shall come near the Lord." Aaron was below him, Nadab and Abihu below Aaron, and the seventy elders below Nadab and Abihu, and the rest below the latter, each one according to his degree of perfection. (Friedlander translation)
Guide for the Perplexed 2:33
IT is clear to me that what Moses experienced at the revelation on Mount Sinai was different from that which was experienced by all the other Israelites, for Moses alone was addressed by God, and for this reason the second person singular is used in the Ten Commandments; Moses then went down to the foot of the mount and told his fellow-men what he had heard. Comp., "I stood between the Lord and you at that time to tell you the word of the Lord" (Deut. v. 5). Again, "Moses spake, and God answered him with a loud voice" (Exod. xix. 19). In the Mechilta our Sages say distinctly that he brought to them every word as he had heard it. Furthermore, the words, "In order that the people hear when I speak with thee" (Exod. xix. 9), show that God spoke to Moses, and the people only heard the mighty sound, not distinct words. It is to the perception of this mighty sound that Scripture refers in the passage, "When ye hear the sound" (Deut. v. 20); again it is stated, "You heard a sound of words" (ibid. iv. 12), and it is not said "You heard words"; and even where the hearing of the words is mentioned, only the perception of the sound is meant. It was only Moses that heard the words, and he reported them to the people. (Friedlander translation, my emphasis)
Thus it seems that according to Rambam himself, the regular people only heard a sound. So in what sense is this different from other miracles? Here they witnessed a miraculous sound, and elsewhere they witnessed other miraculous phenomena. On what basis, then, does Rambam maintain that the revelation at Sinai was qualitatively different from other wonders, such that the former is a proof to Moshe being the messenger of God while the latter is not?
(I am aware of this related question, but I do not believe it is a duplicate. That question is simply asking how we know the revelation at Sinai wasn't a trick. My question is how Rambam distinguishes the believability of the revelation at Sinai from the believability of other miracles. Indeed, the answers to the other question would not work according to my portrayal of Rambam here. I am also aware of this related question, but that one only asks how magic could be faked according to Rambam, not what the difference was between the revelation at Sinai and other miracles.)