A.T. Robertson Commentary John 12:39

"For this cause they could not believe, for that Isaiah said again," — John 12:39 (ASV)

For this cause they could not believe (δια τουτο ουκ εδυναντο πιστευειν). Τουτο (this) seems to have a double reference (to what precedes and to what follows) as in 8:47. The negative imperfect (double augment, εδυναντο) of δυναμα. John is not absolving these Jews from moral responsibility, but only showing that the words of Isaiah "had to be fulfilled, for they were the expression of Divine foreknowledge " (Bernard).