A protected passed pawn ties the enemy king permanently to its square, freeing the attacking king to go and win material elsewhere.
White has a protected passed pawn on e5 (guarded by f4) plus the f4-pawn; Black has an a-pawn and an f5-pawn that is blocked. Both sides have a passed pawn, but they are not equal. Black's king on d7 must stay within reach of e6/e7/e8 for ever, because the e-pawn can advance the moment he leaves, and he can never capture it. White's king, by contrast, is free.