Exodus 13:21

There was only one pillar, which in daylight had the appearance of smoke and by night glowed with fire: see Exodus 14:20; Exodus 14:24. It was the symbol of the divine presence with the host (see on Exodus 3:2), and was their signal and guide on the march: see Exodus 40:34, and cp. Numbers 9:15. It is clearly understood here to be miraculous. It was usual to carry fire signals at the head of an army on the march in early times. Go by day and by (RV) night] It is suggested that the Israelites marched during part of the night as well as by day: cp. Numbers 9:21.