30 The Holy Gospel narrates that when Jesus was crucified "there was darkness over the whole earth" ( Matthew xxvii. 45); a terrifying symbol of what happened and what still happens spiritually wherever incredulity, blind and proud of itself, has succeeded in excluding Christ from modern life, especially from public life, and has undermined faith in God as well as faith in Christ. The consequence is that the moral values by which in other times public and private conduct was gauged have fallen into disuse; and the much vaunted civilization of society, which has made ever more rapid progress, withdrawing man, the family and the State from the beneficent and regenerating effects of the idea of God and the teaching of the Church, has caused to reappear, in regions in which for many centuries shone the splendors of Christian civilization, in a manner ever clearer, ever more distinct, ever more distressing, the signs of a corrupt and corrupting paganism: "There was darkness when they crucified Jesus" (Roman Breviary, Good Friday, Response Five).
Source: Summi Pontificatus (Vatican.va)