Exodus 19:23

And Mosheh said before the Lord, The people cannot come up to mount Sinai, because Thou didst instruct us, saying, Make limits to the mount, and sanctify it.

'ויאמר משה אל ה' לא יוכל העם וגו, the one who interprets the Torah as quoting Moses saying these words, i.e. “You have already told us to fence off the mountain etc. (verse 12) so how could anyone ascend it?” is in error. [a rejection of Rashi’s commentary who understands the word יוכל as “having permission.” Ed.] There is nothing wrong with repeating warnings to people when the time of paying with their lives for warnings which they have ignored draws near. G’d Himself repeated instructions to Moses in verse 24 when He told him to descend and to allow only Aaron to approach a little closer to the mountain. What news did this verse contain? The point is that Moses’ remarks were a question. He asked if G’d had added an additional restriction to what He had issued on the previous two days when He had said in verse 12 that touching the mountain would prove lethal?שלא יוכל העם לעלות אל הר סיני, Moses wanted clarification of the expression פן יהרסו ממנו רב, as opposed to השמרו לכם עלות בהר. He wanted to know if not only touching the mountain was forbidden on pain of death but even approaching it from a relative distance. G’d told him that while it was all right for Aaron to approach a little closer, neither the priests nor the people at large were allowed to come within a certain distance of the base of the mountain. They would ignore such warnings at their peril. He added that even Moses himself would not be granted a visual revelation, he had only been commanded to ascend the mountain in the thick cloud.

וקדשתו, the term is used here as in Exodus 3,5 when Moses was warned not to step on “holy” ground with his sandals as this might prove fatal. Similarly, here; the people had been told that neither man nor beast would survive touching the mountain. [during this period. Ed.]