Jamieson, Fausset and Brown on Exodus 24:18

18. Moses went into the midst of the cloud--the visible token of God's presence. Divine grace animated and supported him to enter with holy boldness.

Moses was in the mount forty days and forty nights--The six days spent in waiting are not included. During that protracted period he was miraculously supported (De 9:9), on a peak scarcely thirty paces in compass.