15 In order to enkindle the zeal of the ministers of God, We again insist on the need to reach the ever-increasing numbers of those who know nothing at all of religion, or who possess at most only such knowledge of God and Christian truths as befits idolaters. How many there are, alas, not only among the young, but among adults and those advanced in years, who know nothing of the chief mysteries of faith; who on hearing the name of Christ can only ask? "Who is he. . . that I may believe in him?" In consequence of this ignorance, they do not consider it a crime to excite and nourish hatred against their neighbor, to enter into most unjust contracts, to do business in dishonest fashion, to hold the funds of others at an exorbitant interest rate, and to commit other iniquities no less reprehensible. They are, moreover, ignorant of the law of Christ which not only condemns immoral actions but also forbids deliberate immoral thoughts and desires. Even when for some reason or other they avoid sensual pleasures, they nevertheless entertain evil thoughts without the least scruple, thereby multiplying their sins above the number of the hairs of the head. These persons are found, we deem it necessary to repeat, not merely among the poorer classes of the people or in sparsely settled districts, but also among those in the higher walks of life, even, indeed, among those puffed up with learning, who, relying upon a vain erudition, feel free to ridicule religion and to "deride whatever they do not know."
Source: Acerbo Nimis (Vatican.va)