I have been allowed to talk with many scholars after their departure from our world, with some who were quite renowned and celebrated throughout the learned world for their publications, as well as with some who were not so well known but who still had within themselves a hidden wisdom.
The ones who at heart denied the Deity, whether or not they acknowledged the Deity out loud, had become so stupid that they could scarcely understand any civic truth, let alone any spiritual truth. I could both comprehend and see that the inner levels of their minds were so shut off that they looked inky black (things like this are made visible in the spiritual world), and that this meant they could not bear any heavenly light or let in any inflow from heaven. The blackness that enveloped their deeper levels was greater and more extensive for people who had convinced themselves of their opposition to the Divine by means of their secular scholarship.
In the other life, people like this gladly accept anything false. They soak it up like a sponge soaking up water; and they repel anything true the way something bony and springy repels anything that falls on it. It is also said that if people convince themselves of their opposition to the Divine and their advocacy of nature, their deeper levels actually become bony. Their heads even look callused, as though they were made of ebony, and this reaches all the way to their noses, a sign that they no longer have any perception.
People like this are sunk in quagmires that look like swamps, where they are pestered by the hallucinations that their falsities turn into. Their hellfire is their craving for glory and fame, which leads them to denounce each other and to torment with hellish zeal anyone who does not worship them as gods. They do this to each other by turns. This is what becomes of all earthly learning that does not accept light from heaven into itself by our acknowledgment of the Divine.
from Heaven and Hell, Section 354