Defending by Changing the Critical Squares

      It's White's move and taking the opposition would be a mistake as after 1.Kg2 Kf4; 2.Kf2 Kxe4, White loses the e-pawn.  Furthermore, Black's King would then occupy one of the f6-pawns critical squares guaranteeing him a win.

     So White figures; if I can't save my e-pawn, I at least better secure the draw.  So White pushes the pawn to e5.  Black's pawn is forced to capture and winds up one rank farther up the board thereby changing it's critical squares to d3, e3 and f3.  Since White's King is now closer to the new critical squares, it can prevent Black's King from occupying them and thereby secure the draw.