Shemot 14:19 And the malach of G-d, who went before the camp of Yisrael, moved and went behind them; and the pillar of cloud went from before them and stood behind them.
The pillar of cloud which had been leading the Benei Yisrael through the desert now moved to their rear. This was to separate the Benei Yisrael from the Egyptians. The Egyptians were shooting arrows and catapulting stones into the camp of the Benei Yisrael, but all these missles were absorbed by the pillar of cloud. (Targum Yonatan; Zohar; Rashi)
Normally, the pillar of cloud would remove itself at night, making way for the pillar of fire (13:21), but on this seventh night of Pesach, the pillar of cloud did not depart. Instead, it moved to the rear of the camp of the Benei Yisrael, separating them from the Egyptians. (Rashi)
The pillar was half dark and half glowing. The dark, cloudy side was toward the Egyptians, while the glowing side faced the Benei Yisrael. Since the Egyptains were in total darkness, they could not even see to aim their weapons. They were totally disoriented.
(Targum Yonatan; Targum Yerushalmi; Midrash, Tehillim 27)
