Now we must consider that God is the universal cause of the enlightening of souls, according to John 1:9:  “That was the true light which enlighteneth every man that cometh into this world,” even as the sun is the universal cause of the enlightening of bodies, though not in the same way; for the sun enlightens by necessity of nature, whereas God works freely, through the order of His wisdom.  Now although the sun, so far as it is concerned, enlightens all bodies, yet if it be encountered by an obstacle in a body, it leaves it in darkness, as happens to a house whose window-shutters are closed, although the sun is in no way the cause of the house being darkened, since it does not act of its own accord in failing to light up the interior of the house; and the cause of this is the person who closed the shutters.  On the other hand, God, of His own accord, withholds His grace from those in whom He finds an obstacle:  so that the cause of grace being withheld is not only the man who raises an obstacle to grace; but God, Who, of His own accord, withholds His grace.  In this way, God is the cause of spiritual blindness, deafness of ear, and hardness of heart.

These differ from one another in respect of the effects of grace, which both perfects the intellect by the gift of wisdom, and softens the affections by the fire of charity.  And since two of the senses excel in rendering service to the intellect, viz. sight and hearing, of which the former assists “discovery,” and the latter, “teaching,” hence it is that spiritual “blindness” corresponds to sight, “heaviness of the ears” to hearing, and “hardness of heart” to the affections.

Reply Obj. 1:  Blindness and hardheartedness, as regards the withholding of grace, are punishments, and therefore, in this respect, they make man no worse.  It is because he is already worsened by sin that he incurs them, even as other punishments.

Reply Obj. 2:  This argument considers hardheartedness in so far as it is a sin.

Reply Obj. 3:  Malice is the demeritorious cause of blindness, just as sin is the cause of punishment:  and in this way too, the devil is said to blind, in so far as he induces man to sin. ________________________

FOURTH ARTICLE [I-II, Q. 79, Art. 4]

Whether Blindness and Hardness of Heart Are Directed to the Salvation of Those Who Are Blinded and Hardened?

Objection 1:  It would seem that blindness and hardness of heart are always directed to the salvation of those who are blinded and hardened.  For Augustine says (Enchiridion xi) that “as God is supremely good, He would nowise allow evil to be done, unless He could draw some good from every evil.”  Much more, therefore, does He direct to some good, the evil of which He Himself is the cause.  Now God is the cause of blindness and hardness of heart, as stated above (A. 3).  Therefore they are directed to the salvation of those who are blinded and hardened.