פירוש על שמות 10:22

שלשת ימים denotes a triad of days. old French terziane; so, too, שבעת ימים everywhere it occurs denotes in old French a septaine of days (a period of seven days).

חשך אפלה, a combination of regular darkness (absence of sunlight), plus added deep darkness.

ויט משה את ידו, "Moses inclined his hand, etc.," We need to understand why Moses had used his staff to bring about the plague of locusts (verse 13) when G'd had told him to incline only his hand (verse 12). There had not been a single plague so far which was introduced by Moses being told to use "his hand" rather than his staff.