Only here by Paul. See on hard, Mat 25:24; see on Jud 1:14; see on Jam 3:4. Three words are used in the Hebrew to describe the hardening of Pharaoh's heart. The one which occurs most frequently, properly means to be strong, and therefore represents the hardness as foolhardiness, infatuated insensibility to danger. See Exodus 14. The word is used in its positive sense, hardens, not merely permits to become hard. In Exodus the hardening is represented as self-produced (Exo 8:15, Exo 8:32; Exo 9:34), and as produced by God (Exo 4:21; Exo 7:3; Exo 9:12; Exo 10:20, Exo 10:27; Exo 11:10). Paul here chooses the latter representation.