ציטירנדיקער פּירוש אויף איוב 2:5

על פני, “in My place;” we find a similar use of this expression in Deuteronomy 21,16: על פני בן השנואה, where the Torah forbids to treat the firstborn son of a beloved wife, that has been born later than the firstborn son of a less beloved wife, preferentially. In other words, as long as the firstborn son of the less beloved wife is alive, his claim to be treated as the firstborn of the father cannot be overruled. We also have this expression when after the death of the two oldest sons of Aaron, Nadav and Avihu, his sons Elazar and Ittamar were appointed as priests in their stead. An alternate explanation: “If you were to accept any of these deities as your gods this would be against My express wishes and would arouse My anger against you.” An example of a similar construction would be: חמס ושוד ישמע על פני, “before Me constantly are grief and wounds.” Or: ,אם לא אל פניך יברכך, “if not he will curse you to your face.” (Job 2,5)

.'ויחזק ה, G’d needed to reinforce Pharaoh’s heart as without this he would not have been able to endure this plague without his resistance collapsing. We know how Satan expected Job to react to the same affliction, from Job 2,5 “if You lay a hand on his bones and flesh he will surely blaspheme.”