1)
Why do the Makos follow a set pattern? In the first out of each set of three Makos, Moshe confronted Pharaoh at the Nile; in the second (such as this plague of Dever), it was at the palace; whereas the third had no warning at all?
1.
Maharal: Refer to 7:14:8:2, regarding the Makos' breakup into the categories De'tzach, A'dash, Be'achav.
