11 It is needful, therefore, Venerable Brethren, that we should unflinchingly set up "a wall for the house of Israel" ( Ezechiel xiii. 5), and that we too should join all our forces together into one solid band against these hostile ranks which are hostile both to God and to mankind. For in this fight we are contending for the greatest question that can be proposed to human liberty: either for God or against God; here, again, is a debate in which the fate of the whole world is concerned; for in every matter, in politics, in economics, in morals, in discipline, in the arts, in the state, in civic and domestic society, in the East and in the West, everywhere we meet with this debate, and its consequences are a matter of supreme moment. And so it comes to pass that even the masters of that sect which foolishly says that the world is nothing but matter, and boasts that it has already shown for certain that there is no God - even these are constrained, again and again, to institute discussions about Him, though they thought they had done away with Him altogether.
Source: Caritate Christi Compulsi (Vatican.va)