"And the LORD said to him, 'Go down, and you shall come up'" (Exodus 19:24). You might think all could go up with him; therefore Scripture teaches, "but let not the people break through to come up" (Exodus 19:24). You might think the priests could go up with him; therefore Scripture teaches, "and you shall come up, you and Aaron with you" (Exodus 19:24) and the priests are not with you. You might think Aaron was within the same partition [as Moses]; therefore Scripture teaches, "and Moses alone shall approach the LORD" (Exodus 24:2). Say from now on: Moses had a partition to himself and Aaron had a partition to himself.
Moses and Aaron Each Granted a Separate Boundary on Sinai
Mekhilta DeRabbi Shimon Ben Yochai 19:24
ויאמר אליו ה' לך רד ועלית אתה יכול הכל עלו עמו ת"ל והעם אל יהרסו לעלות: יכול הכהנים עלו עמו ת"ל ועלית אתה ואהרן עמך ואין הכהנים עמך: יכול אהרן במחיצה ת"ל (כ"ד ב') ונגש משה לבדו אל האלהים אמור מעתה משה מחיצה לעצמו ואהרן מחיצה לעצמו: