Spiritual blindness is a disease of intellectuals, those people who are the most likely to have escaped the lure of materialism. It is about the worst thing that would happen to those whose lives center in the mind.
First, what is it? It is a punishment inflicted by God for intellectual sins. The sins are intellectual curiosity and pride. The punishment consists in this: that God takes away His light from the minds of those who do not wish to receive it, abandoning them to the darkness which original sin and their own sins pull down upon them. Spiritual blindness is characterized not by ignorance of facts (which is a relatively clear and easily remedial state), nor by native stupidity, but by confusion of thought and defect of judgement. ... Garriou-Lagrange says of spiritual blindness: “It takes all penetration away from us and leaves us in a state of spiritual dullness, which is like the loss of all higher intelligence.”
There are several ways of recognizing spiritual blindness. It is chiefly marked by mental confusion and the inability to recognize implications and contradictions. It also consists in a preference for discussing the trivial over the important, the material rather than the spiritual.
Carol Robinson, My Life with Thomas Aquinas, Angelus Press, 1995, pp. 190-191
"So let us be confident, let us not be unprepared, let us not be outflanked, let us be wise, vigilant, fighting against those who are trying to tear the faith out of our souls and morality out of our hearts, so that we may remain Catholics, remain united to the Blessed Virgin Mary, remain united to the Roman Catholic Church, remain faithful children of the Church."- Archbp. Lefebvre 1980