רואים את הקולות
G-d’s revelation through open and revealed miracles has the ability to affect man’s view and understanding of the world, to heighten his outlook on the world around him and his relationship to it. Our Sages say "שהיו רואין את הנשמע ושומעין את הנראה" they were able to see the sounds and hear the sights. They were also able to point at G-d and say "זה קלי ואנוהו", this is my G-d and I will glorify Him.
A deep concept is gleaned from this. The Nefesh Hachaim explains that of all the senses with which man has been blessed by G-d, sight is the most accurate. Anything which a person has seen with his own eyes, he has not even a shadow of a doubt in his heart as to the authenticity of that thing’s existence. With other senses—hearing, for example—a person might hear something but not be absolutely certain as to what it is he heard, or its authenticity. Our Sages say "לא תהא שמיעה גדולה מראיה", the hearing should not be greater than the sighting. But Bnei Yisrael, children of G-d who cling to the faith of their fathers, know that eyesight is not what determines the truth of something’s existence. Even G-d, because of Whom all things in existence in the heavens and the earth and in between is in existence solely because of His existence, said "כי לא יראני האדם וחי", for no human can see Me and live. Thus, our eyes do not even see the essence of the ultimate Existence!
What really does man amount to, if not the soul which resides within him, the soul which his Creator breathed into him—and the soul is not even visible! Our eyes cannot see the ministering angels who are carrying out G-d’s will in His world, or the demons and spirits who hover in space. We know these things to exist because our fathers have told us so, and we’ve received the tradition from our holy teachers in each generation. The ספר החינוך writes in his introduction that the basis of our faith is the tradition that has been passed down from father to son, generation to generation, even though these things are not visible to the human eye.
When our forefathers stood at Har Sinai they attained a level of spirituality whereby they were able to see the sounds, meaning that they believed what they had heard as though they had actually seen it. They heard that which is seen, the whole physical world was so removed from their consciousness and feelings that it was as if it were only hearsay, not truly verifiable.
Based on the above we can explain what is brought in the following Gemara:
R’ Yochanan once sat and lectured: the Holy One, Blessed is He, will one day bring precious stones and pearls which are thirty amos by thirty amos, and He will cut out from them an opening of ten amos by twenty amos, and He will place them at the gates of Jerusalem. A certain student mocked him for discussing such incredible occurenes. The student said: now, we cannot find precious stones and pearls even the size of an egg of a small dove, can stones of such an immense size ever be found? After a time the student’s ship set sail upon the sea, and he saw ministering angels sitting and sawing precious stones and pearls that were thirty amos by thirty amos, and ten amos by a height of twenty amos was cut from them. The student said to the ministering angels, For whom are these? They told him that the Holy One Blessed is He, will one day place them at the gates of Jerusalem. The student came back before R’ Yochanan and said to him, My Master! Continue to lecture! You are fit to lecture. Just as you said, so I saw. R’ Yochanan said to him: You empty person! Had you not seen it yourself would you not have believed it? You are one who mocks the words of the Sages. R’ Yochanan set his eyes upon him and the student became a heap of bones.
It is interesting to note that the student was not punished for mocking the words of his teacher R’ Yochanan, but rather was punished when he returned to R’ Yochanan to confirm what he had said. This warrants explanation, but based on what we’ve learned we can understand. When the student came back to R’ Yochanan and expressed his amazement and excitement for what he saw, he said “just as you (R’ Yochanan) said, so I saw.” By saying this he showed that through his seeing with his own eyes he believed what R’ Yochanan had said, and therefore he retracted his mockery of R’ Yochanan’s initial words to him. R’ Yochanan got angry with him and said “You empty person! Had you not seen it yourself would you not have believed it?” R’ Yochanan was rebuking his student for not believing the words of the Torah. Is it our eyes—what we see before us—that determine whether we believe something, or the Torah which we hear with our ears that determines what we believe? For this the student was punished, because someone of his stature (and surely he was of a great caliber—he had witnessed ministering angels and even conversed with them), should be able to “see the sound,” to believe that which his ears hear, and know it to be true as if he had seen it.
The student’s punishment was measure for measure, and in it we see a reminder of his transgression. To the naked eye, a human being is merely a heap of bones. Yet we know that his life comes solely from the power of his divine soul which sustains him and makes him alive. Because the student valued only that which his eyes were able to see, he was turned into a heap of bones, measure for measure. This is why R’ Yochanan said to him You empty person! Do you not admit that you have a soul in you although it cannot be seen? Why can’t you “see” i.e. believe, what is heard, instead of only “hearing”, i.e. believing, what you see?
We find that it was characteristic of R’ Yochanan to impart to his students that there is no truth like the truth of Torah, even when things appear to be in complete opposition to reality. Says the Gemara,
[R’ Yitzchak] said to [Rav Nachman]: Thus said R’ Yochanan: Yaakov Avinu never died. [Rav Nachman] said to [R’ Yitzchak]: Was it for naught that the eulogizers eulogized him and the embalmers embalmed him and the buriers buried him!? [R’ Yitzchak] replied to [Rav Nachman]: I am expounding a verse etc.
Rashi explains that Yaakov really didn’t die, but that to the embalmers and eulogizers he appeared dead. Expounding on a verse, R’ Yochanan said that Yaakov Avinu didn’t die, although this seems to contradict reality.
The Gemara relates how
Rav Sheishes was full of light (i.e. blind). Everyone was going to greet the king. Rav Sheishes rose and went with them. A certain Sadducee met [Rav Sheishes], and said to him “whole pitchers go to the river. Where do broken [pitchers] go?” [Rav Sheishes] answered him, “come and see that I know more about the king’s procession than you do.” The first troop passed. When it became loud, that Sadducee said to [Rav Sheishes], “the king has come!” Rav Sheishes said to him, “he is not coming.” A second troop passed by. When it became loud, that Sadducee sais to Rav Sheishes, “now the king is coming!” Rav Sheishes said to him, “the king is not coming.” A third [troop] passed by. When it subsequently grew quiet, Rav Sheishes said to him, “It is now certain that the king is coming.” That Sadducee asked him, “how do you know this?” He answered him, “for the royalty of earth is a reflection of the royalty of Heaven. Hence I knew that the king would come when it grew quiet after three troops passed by because it is written regarding the royalty of Heaven: ‘Go out and stand on the mountain before Hashem. And behold, Hashem was passing, and a great powerful wind, smashing mountains and breaking rocks, went before Hashem; Hashem was not in the wind. After the wind came an earthquake; Hashem was not in the earthquake. After the earthquake came a fire; Hashem was not in the fire. After the fire came a still, thin sound.’” When the king finally came, Rav Sheishes began blessing him. That Sadducee said to him, “someone you cannot see you are blessing!” What became of that Sadducee? Some say that his colleagues painted his eyes. And some say that Rav Sheishes set his eyes upon him and he became a heap of bones.
This, too teaches us a profound lesson, that what our eyes see does not determine the absolute truth, rather what we hear. Rav Sheishes who was blind not only understood spiritual matters better than the Sadducee but understood earthly matters better than him too. When the Sadducee did not learn a lesson, stayed put in his ways to value “seeing” as the uppermost sense and to disregard Rav Sheishes by asking him “someone you cannot see you are blessing!” he was punished measure for measure and his eyes were painted or became a heap of bones as mentioned above.
Based on this we can explain what the passuk states "את קולך שמעתי בתוך הגן ואירא כי ערום אנכי", I heard the sound of You in the garden and I was afraid because I am naked. Adam did not merit seeing the voice of G-d but only heard it, and that is why he was afraid. But in future times we will merit "כי עין בעין יראו בשוב ה' ציון וראו כל בשר יחדיו כי פי ה' דבר" with their own eyes they will see that Hashem returns to Zion, and all flesh together will see that the mouth of Hashem has spoken. "והוא ישמיענו ברחמיו שנית לעיני כל חי לאמר, and He will let us hear, in His compassion, for a second time in the presence of all the living. We will once again be able to see the sounds when G-d will let us hear in the presence of all the living. Perhaps this is why we are commanded "השמר לך... פן תשכח את הדברים אשר ראו עיניך", beware and guard yourself lest you forget the things your eyes have seen, which it does not mention by remembering the Exodus or any of the other six daily remembrances.
 מכילתא פרשת יתרו
 נפש החיים שע"ג פי"א בהג"ה
 ראש השנה כ"ה ע"ב
רמב"ם הלכות יסודי התורה פ"א ה"א
 For further insight see the Ramban on דברים ד':ט'.
 For further insight see the משך חכמה on פרשת חקת and the מאור עינים on פרשת בשלח where each of them writes that we must ensure the power of hearing overpowers the power of seeing.
 בבא בתרא ע"ה ע"א
 תענית ה' ע"ב
 The מהרש"א explains that although his body died, his soul did not.
 ברכות נ"ח ע"א
 בראשית ג':י'
 ישעיה נ"ב: ח'
 ישעיה מ': ה'
ויו"ט קדושה למוסף של שבת
 דברים ד': ט'
 According to the Ramban במצוות ששכח הרב ל"ת ב' this is a negative commandment. Also see אגרת תימן לרמב"ם