"And the LORD said to Moses, 'Go down, warn the people'" and so forth (Exodus 19:21). The one who had gone up—urge him not to look; and the one who had not gone up—urge him not to go up. "Lest they break through to the LORD to see"—that they should not break down the boundaries. "And many of them fall." "Many" means nothing but a multitude. This tells that if one of them fell to the ground, He accounts it to him as though a multitude had fallen before Him. Another interpretation: "And many of them fall"—of Him whose smaller part holds back His larger part [i.e., even the loss of a few is reckoned as the loss of the whole].
Warning the People Not to Break Through to See the LORD
Mekhilta DeRabbi Shimon Ben Yochai 19:21
ויאמר ה' אל משה רד העד בעם וגו' מי שעלה זרזו שלא יראה ומי שלא עלה זרזו שלא יעלה: פן יהרסו אל ה' לראות. שלא יפגרו את התחומין: ונפל ממנו רב. אין רב אלא אכלוסין מגיד שאם נפל אחד מהן לארץ מעלה עליו כאלו אכלוסין לפניו: ד"א ונפל ממנו רב ממי שמיעוטו מעכב את רובו: