5 Nor let the world excuse itself by this, that it is hindered by the devil from believing on Christ. For to believers the prince of the world is cast out, that he work no more in the hearts of men whom Christ has begun to possess by faith; as he works in the children of unbelief; whom he is constantly stirring up to tempt and disturb the righteous. For because he is cast out, who once had dominion interiorly he wages war exteriorly. Although then by means of his persecutions, “the Lord does direct the meek in judgment;” nevertheless in this very fact of his being cast out, is he “judged already.”
And of this, “judgment” is the world convinced; for in vain does he who will not believe in Christ complain of the devil whom, judged, that is, cast out, and for the exercising of us allowed to attack us from without, not only men, but even women, and boys, and girls, Martyrs have overcome. Now in whom have they overcome, but in Him on whom they have believed, and whom seeing not, they loved, and by whose dominion in their hearts they have got rid of a most oppressive lord. And all this by grace, by the gift, that is, of the Holy Ghost.
Rightly then does the Same Spirit convince the world, both of “sin,” because it believes not on Christ; “and of righteousness,” because they who have had the will have believed, though Him on whom they believed they saw not; and by His Resurrection have hoped that themselves also should be in the resurrection perfected; “and of judgment,” because if they had had the will to believe, they could be hindered by none, “for that the prince of this world has been judged already.”
Source: Sermons on Selected Lessons of the New Testament (New Advent)