11 But when he added, “And they should be converted, and I should heal them,” is there a “not” to be understood, that is, they should not be converted, connecting it with the clause before, where it is said, “that they should not see with their eyes and understand with their heart;” for here also it is certainly meant, “and should not understand”? For conversion itself is likewise a gift of His grace, as when it is said to Him, “Turn us, O God of Hosts.” Or may it be that we are to understand this also as actually taking place through the merciful experience of the divine method of healing, [namely this,] that, being of proud and perverse wills, and wishing to establish their own righteousness, they were left alone for the very purpose of being blinded; and thus blinded in order that they might stumble on the stone of stumbling, and have their faces filled with shame; and so, being thus humbled, might seek the name of the Lord, and no longer a righteousness of their own, that inflated their pride, but the righteousness of God, that justifies the ungodly?
For this very way turned out to the good of many of them, who were afterwards filled with remorse for wickedness, and believed on Christ; and on whose behalf He Himself had put up the prayer, “Father, forgive them, for they know not what they do.” And it is of that ignorance of theirs also that the apostle says, “I bear them record that they have a zeal of God, but not according to knowledge:” for he then goes on also to add, “For they, being ignorant of God's righteousness, and seeking to establish their own righteousness, have not submitted themselves unto the righteousness of God.”
Source: Tractates on the Gospel of John (New Advent)