The ninth plague, like the third and the sixth, was inflicted without prior warning. After the plague of boils, God had announced that He was about to send all His plagues upon the “heart” of the king (ch. 9:14). A succession of judgments was therefore to be expected. Apparently, this plague quickly followed the eighth.

 Some commentators have assumed that an eclipse of the sun caused the intense darkness. This interpretation, however, cannot be correct, inasmuch as an eclipse could never produce darkness lasting for three days (v. 22). The majority of interpreters have felt that the miracle was wrought through the chamsin, a desert sandstorm that occasionally blows over Egypt and covers the land with a weird darkness. This is due to dense clouds of fine sand that the wind carries with it and that intercept the light of the sun, producing darkness deeper than that of the worst fogs. The present writer once experienced such a sandstorm at the edge of the Indian Desert on a clear day, and can testify that for half an hour darkness prevailed equal to that of a moonless night. Saturated with fine particles of sand, the wind was most annoying and depressing, and men and beasts looked for cover. The fine sand penetrated every room and even the closets of the houses. A sandstorm may blow for two or three days, but it seldom has so extreme an effect for very long at a time. Even if God used swirling sand to produce the darkness, it was nonetheless miraculous, because though the entire country was enveloped in impenetrable darkness for three days, the children of Israel, living in that same country, had light (v. 23). But the Egyptians were accustomed to severe sandstorms blowing in from the desert. Furthermore, with each of the other plagues Moses describes the agency by which it was accomplished, and it would be logical here to expect him to refer to it as a sandstorm if that is what he meant.

Like the previous plagues, this one dealt a heavy blow to the Egyptian gods. The sungod Ra had been the chief god of Egypt for centuries, and every king called himself the “son of Ra.” In the time of Moses this god was identified with Amen and bore the name Amen-Ra. The greatest temples the world has ever seen were built in his honor, and one of them, the great temple at Karnak in Upper Egypt, is still magnificent, even in a state of ruin. Another god was the sun disc Aten, which a few decades after the Exodus became, briefly, the supreme god of the Egyptian religious system. By the ninth plague the utter impotence of these gods was clearly demonstrated to their worshipers.