PILLAR OF CLOUD AND PILLAR OF FIRE - The visible symbol of the presence of God caused a panic among the Egyptians as it cut them off from the Israelites, and continued to guide and protect the latter uninterruptedly throughout their wanderings. The Israelites were protected against the elements and wild beasts; even their garments did not wear out or become dirty.

.

Theophanies

Pillar of Cloud and Pillar of Fire 

.

The earliest traditions of the Exodus from Egypt refer to the pillar of cloud by day and of fire by night, which accompanied the Children of Israel on their way through the desert (Exodus 13:21–22).

The visible symbol of the presence of God caused a panic among the Egyptians as it cut them off from the Israelites, and continued to guide and protect the latter uninterruptedly throughout their wanderings (Exodus 14:19b, 24a).

Later generations remembered it as a special sign of divine favor, no less important than the parting of the Sea of Reeds itself (cf. Ps. 78:14).

Another early tradition connected the cloud with the Tent of Meeting.

According to the view attributed by critics to the author of the Elohist account (E), the pillar of cloud served not as a regular escort marching at the head of the people, but as an intermittent presence, descending from time to time to the entrance of the Tent of Meeting when God conversed with Moses (Exodus 33:9–10; Numbers 11:25; 12:5).

The priestly authors, on the other hand, taught that "a cloud of the Lord" (not a pillar) with a fiery appearance by night, permanently covered the Tabernacle from the day of its completion, lifting only to signal the breaking of camp for a new journey (Exodus 40:34–38; Numbers 9:15–23; 10:11–12, 34; 14:14).

The Divine Presence in Solomon's Temple was similarly accompanied by the descent of the cloud  though the pillar of cloud and of fire did not accompany the Israelites into the Promised Land (I Kings 8:10–11; cf. Exodus 16:10; Leviticus 16:2).

Various explanations have been sought for the origin of these traditions. Among them is the attested use of braziers filled with burning wood at the head of caravans or armies, sometimes placed before the tent of the chief or carried before him.

Others derive the imagery from the pillars before Solomon's Temple, which, they contend, were fiery cressets emitting clouds of smoke and flame by day and by night at the time of a festival.

Still others point to the smoke that rose from the altar of the burnt offering as the origin of the representation.

The most commonly accepted theory connects the pillar of cloud and fire with the theophany at Sinai, when the descent of the Lord was marked by a thick cloud, by thunder, lightening, smoke, and fire. (Exodus 19:9)

Attempts to provide a natural basis for this narrative have pointed to the possible existence of volcanic action in the vicinity of Sinai – which is highly unlikely – or to the sudden outbreak of a raging desert storm.

In any event, there can be little doubt that the imagery is as old as the time of Moses, and that the cloud, and, in a lesser degree, the fire symbolism proved effective in communicating the presence of God to the people.

Post-biblical legend embellished the biblical account. 

Thus, not one but seven clouds descended at Sukkot to envelop and protect the Israelites, one on each of the four sides of the camp, one above and one below, and one which went before them to raise the valleys and lower the mountains.

The Israelites were protected against the elements and wild beasts; even their garments did not wear out or become dirty.

http://www.jewishvirtuallibrary.org/jsource/judaica/ejud_0002_0016_0_15772.html