Sforno on Exodus 9:12/ספורנו על שמות ט׳:י״ב

1.'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.”