2 Yet in speaking of the light of faith, we can almost hear the objections of many of our contemporaries. In modernity, that light might have been considered sufficient for societies of old, but was felt to be of no use for new times, for a humanity come of age, proud of its rationality and anxious to explore the future in novel ways. Faith thus appeared to some as an illusory light, preventing mankind from boldly setting out in quest of knowledge. The young Nietzsche encouraged his sister Elisabeth to take risks, to tread "new paths… with all the uncertainty of one who must find his own way", adding that "this is where humanity’s paths part: if you want peace of soul and happiness, then believe, but if you want to be a follower of truth, then seek". Belief would be incompatible with seeking. From this starting point Nietzsche was to develop his critique of Christianity for diminishing the full meaning of human existence and stripping life of novelty and adventure. Faith would thus be the illusion of light, an illusion which blocks the path of a liberated humanity to its future.
Source: Lumen Fidei (Vatican.va)