Exodus 13:21-22

And the LORD went before them by day in a pillar of a cloud, to lead them the way; and by night in a pillar of fire, to give them light; to go by day and night:

The Lord went before them - by a visible token of his presence, the Shechinah, in a majestic cloud (Psalms 78:14; Nehemiah 9:12; 1 Corinthians 10:1), called the angel of God (Exodus 14:19; Exodus 23:20; Psalms 99:6; Isaiah 63:8). The rationalistic explanation of this is, that it refers to the ordinary signal given on journeys by the smoke of the caravan fires. Each company, or division of a caravan, is distinguished by an appropriate standard, which at night consists of long poles, surmounted by small eagles or beacons, formed of iron hoops, which are filled with combustible materials for light, to the number of ten or twelve to each company; those of one division being of a different figure and shape from those of another; so that everyone knows, by looking at the standard by night or by day, whether he is in his proper place.

But it will be easily seen that this arrangement does not answer the description given in the sacred narrative, which states that the Israelites were guided on their march not only by pillar of fire by night, but of cloud by day. And if the truthfulness of the record respecting the miraculous means by which the deliverance of the Israelites from Egypt was effected be admitted, the credibility of this portion of the narrative cannot be affected by the relation of a miraculous guidance being afforded them in their exodus from the house of bondage. But it would have been contrary to all right views of the divine conduct to imagine that the Lord, after having in so remarkable a manner interposed for their rescue from oppression and slavery, had abandoned all further interest in their cause the moment their release was accomplished, and therefore the historical character of this book requires, in consistency, the assertion of such a miracle of providential care and protection as is here stated to have been vouchsafed to His people by the visible symbol of the divine presence day and night.

This fact supplies some of the noblest figures in the writings of the Hebrew prophets (Zechariah 8:5: cf. Numbers 10:34; Isaiah 4:5). There was only one cloud (Exodus 14:19; Exodus 14:24; Numbers 9:21), which, consisting doubtless of the same materials as ordinary clouds, and charged with electricity, so far as natural means were employed, assumed the form of a pillar, and occupied a position in the sky sufficiently high to be seen by all in the procession, even to the remotest rear (Deuteronomy 1:33). But neither the form nor the position of the cloud was unchangeable. The cloud first appeared at Etham as their Leader, when entering upon new and unknown tract; and He who went before them was Christ: for he is afterward (Exodus 14:19) called "the angel of God."