Notice the alignment in verse Ex24-01:02 discussing the closeness to God during the revelation:
• And unto Moses He said: 'Come up unto HaShem, thou, and Aaron, Nadab, and Abihu,
• and seventy of the elders of Israel; and worship ye afar off;
and
• Moses alone shall come near unto HaShem; but
• they shall not come near; neither
• shall the people go up with him.'
The aligned verselets indicate three stages of nearness to God during the revelation
• Moses: Comes closest
• The elders: They ascend the mountain but do not come closer
• The nation: They are prohibited from even ascending the mountain

The above alignment clarifies verse Ex19-24 which also discusses the closeness to God during the revelation: And HaShem said unto him: 'Go, get thee down, and
• thou shalt come up, thou, and Aaron with thee;
• but let not the priests and
• the people break through to come up unto HaShem,
lest He break forth upon them.' Hence the Rashi comment:
• The people were prohibited from ascending the mountain
• The elders were allowed to ascend the mountain but were prohibited from coming closer to God (like Moses)
• The people were prohibited from even coming up the mountain.

Sermonic points: The above verses emphasize a doctrinal point of Judaism, the superiority of Mosaic prophecy. For although the elders were allowed to ascend the mountain their prophetic status of closeness to God was not as great as Moses. Since Moses had a higher state of prophecy it was important that the Torah be received by him and not by people with inferior prophetic status.