Exodus 14:20

It was a cloud and darkness to them, etc. - That the Israelites might not be dismayed at the appearance of their enemies, and that these might not be able to discern the object of their pursuit, the pillar of cloud moved from the front to the rear of the Israelitish camp, so as perfectly to separate between them and the Egyptians. It appears also that this cloud had two sides, one dark and the other luminous: the luminous side gave light to the whole camp of Israel during the night of passage; and the dark side, turned towards the pursuing Egyptians, prevented them from receiving any benefit from that light. How easily can God make the same thing an instrument of destruction or salvation, as seems best to his godly wisdom! He alone can work by all agents, and produce any kind of effect even by the same instrument; for all things serve the purposes of his will.