Or HaChaim on Exodus 40:35/אור החיים על שמות מ׳:ל״ה

1 ולא יכול משה לכא אל אהל מועד, and Moses was unable to enter the Tent of Testimony, etc. It seems strange that the "cloud" prevented Moses from entering the Tent seeing that the Torah had told us in Exodus 24,18 that "Moses went inside the cloud, etc." The difference is clear. In Parshat Mishpatim Moses entered the cloud after G'd had summoned him. In this instance no summons from G'd had been forthcoming. Another reason why Moses could not enter the Tent may have been indicated by the words כי שכן עליו הענן, that the cloud was stationary above the Tent and the glory of G'd filled the entire Tent. In Mishpatim we were told (24,17) that G'd's appearance on the top of the Mountain was like that of fire which consumes, and immediately afterwards we were told that Moses entered the cloud prior to ascending the Mountain. This means that the place Moses ascended was not the place where G'd's glory reposed at that time. In our situation, Moses could not enter an area in which G'd's glory reposed.