After Kabbalas HaTorah, Hashem told Moshe Rabbeinu, "So you shall say to Bnei Yisrael, 'You have seen that I spoke to you from Heaven'" (Shemos 20, 19). Rav Wolbe (Shiurei Chumash) comments, that unlike the beliefs espoused by gentile nations, our emunah is founded on what we perceived with our own eyes.
During Kabbalas HaTorah Bnei Yisrael attained a spiritual level that paralleled the spiritual level that existed before Adam sinned. This is what Chazal refer to as "Shechina b'tachtonim" i.e. Hashem's glory resided down here on earth. The closeness is so great that His presence is literally palpable to our senses. Attaining, and thereafter living with, this apex is the very purpose of creation and toward which we strive with every aspect of our avodah.
Rav Wolbe cites the Ramban (ibid. 19, 9) who elaborates on this idea. The Torah tells us, "And Hashem said to Moshe, Behold I will come to you in the thickness of the cloud, so that the nation will hear when I speak to you, and they will also believe in you forever.'" The Ramban explains that the Bnei Yisrael all reached the level of prophecy, and they heard Hashem speaking to Moshe. The reason for this was that they would not have to base their belief on what others had told them, for they had heard with their own ears how Hashem spoke to Moshe. No prophet or diviner will ever be able to deny or contradict Moshe's words, since Bnei Yisrael themselves heard how Hashem gave over His word to Moshe Rabbeinu.
Most religious beliefs are based on what people heard from their fathers and they from their fathers. The Ramban writes that we believe what our parents tell us "because a father will not lie to his son." However, the forefathers of other religions based all of their information on what they were told by others. This is not the case with the Jewish People. Each and every one of the hundreds of thousands of our forefathers heard Hashem speak to Moshe, and thereby acknowledged the veracity of Moshe's prophecies. The foundation of our emunah is so rock solid that it was palpable even to the physical senses.