15 In this error, which is the chief one of our time and the source whence all the others spring, lies the origin of so much loss of eternal salvation among men, and of all the ruins affecting religion which we continue to lament, and of the many others which we still fear will happen if the evil be not remedied. For all supernatural order is denied, and, as a consequence, the divine intervention in the order of creation and in the government of the world and in the possibility of miracles; and when all these are taken away the foundations of the Christian religion are necessarily shaken. Men even go so far as to impugn the arguments for the existence of God, denying with unparalleled audacity and against the first principles of reason the invincible force of the proof which from the effects ascends to their cause, that is God, and to the notion of His infinite attributes. "For the invisible things of him, from the creation of the world, are clearly seen, being understood by the things that are made: his eternal power also and divinity" ( Rom . i. 20). The way is thus opened to other most grievous errors, equally repugnant to right reason and pernicious to good morals.
Source: Iucunda Sane (Vatican.va)