Kommentar zu Schemot 19:21

העד בעם signifies, WARN THEM not to ascend the mountain.

רד העד בעם פן יהרסו, when I will be speaking to them. Perhaps they will think that because they have been found worthy to have prophetic insights that they have attained the level of “face to face” prophecy as had Moses their leader. This could prove fatal if they tried to cross the boundary separating Me from them. Your presence down below will act as additional safeguard.

פן יהרסו אל ה׳ לראות, "lest they break through unto the Lord to gaze;" The Torah means that people should not think that they would catch a glimpse of G'd though they would die in the process; Psalms 63,4 expresses this thought succinctly when David says: "it is better to experience Your faithfulness than life itself." The people would consider their death under such circumstances as the beginning of their true life. The expression פן יהרסו is to be understood as the people's willingness to lose their lives in order to become part of such an experience as gazing at the glory of G'd. ונפל ממנו רב, "and many of them woul fall;" G'd warns that in such a scenario the people would experience a much greater "fall" than they had bargained for. Alternatively, G'd merely warns that if the people would approach to an area out of bounds to them, He would have to reduce the blinding light accompanying the revelation as otherwise they would die from exposure to this light. This then would be the meaning of פן יהרסו אל השם, they would break through towards His light in order to gain a glimpse. This also tells us that the people would not achieve their aim to gaze upon G'd even if they would break through the barrier. It is part of the meaning of the word פן in our verse. In the event that we would have thought that the people's endeavour to gaze upon something they could not see anyway would have neither positive nor negative consequences, the Torah writes ונפל ממנו רב, that it would have very negative consequences for those concerned. The word רב may refer to the leading members of the people. The Torah would then tell us that even the most spiritually advanced of the people would not be allowed to gaze upon the spectacle but they would be punished severely if they tried.