Then Moses went up on the mountain, and the cloud covered the mountain. The glory of the Lord settled on Mount Sinai, and the cloud covered it for six days; on the seventh day he called to Moses out of the cloud. Now the appearance of the glory of the Lord was like a devouring fire on the top of the mountain in the sight of the people of Israel. Moses entered the cloud, and went up on the mountain. Moses was on the mountain for forty days and forty nights.
This passage is a metaphysical description of the sacred process by which Moses assumed leadership of the people of Israel and carried out the divine dictates he received. Both seven days and 40 days and nights are used frequently in the Bible to symbolize the completion of spiritual mandates—from the creation in Genesis to the 40 days of Jesus in the wilderness. They are not necessarily to be taken literally, but rather as indications that the time required was achieved.