“And the L-RD said unto Moses: ‘Stretch out thy hand toward the heaven, that there may be darkness over the land of Egypt, even darkness which may be felt.’ And Moses stretched forth his hand toward the heaven; and there was a thick darkness in all the land of Egypt three days; they saw not one another, neither rose any from his place for three days; but all the children of Israel had light in their dwellings.”– Exodus 10:21-23, JPS 1917 Tanach
Or HaChayim explains that, according to certain rabbinic commentators, the darkness that originated in a heavenly place, may be likened to the description, found in psalms, “He made darkness His hiding-place, His pavilion round about Him; darkness of waters, thick clouds of the skies” (Psalms 18:12, JPS; Shemot Rabbah 14). This verse conveys the understanding, that, H’Shem, who is surrounded by atmospheric darkness, is hidden within those phenomena. This may explain why Moshe raised his hand to the sky, instead of his staff. “Inasmuch as the darkness was of a supernatural kind, Moses did not consider it appropriate to raise his staff against supernatural phenomena” (Ohr HaChayim on Exodus 10:23, sefaria.org).
Another view likens the darkness that encompassed Egypt for three days, to the darkness of purgatory (Or HaChayim on Exodus 10:23; sefaria.org). Or HaChayim comments that both views may be feasible, within the context of the plague’s duration. According to Rashi’s rendering, there were two sets of three-day periods of darkness, since each plague always lasted for a week. So, during the first three days, no person could see another; and, during the second three days, “no one could get up from where he was.” (The third day of darkness occurred at the encampment of the Egyptians, who had pursued B’nei Yisrael to the edge of the Sea of Reeds).
How might these considerations be understood, in a manner of rendering some significance to the comments, beyond their face value? If we consider that H’Shem, Who is surrounded by dark clouds, refers as well to our inability to draw close to Him, unless we enter a place of unknowing, wherein we cannot fully rely on our intellectual understanding of Him, we are gaining understanding of the nature of His essence, as well as our relationship to Him.