59 The Gospel clearly warns us of this difference and the need to keep ourselves distinct from the world. By the world, here, is meant either those human beings who are opposed to the light of faith and the gift of grace, those whose naive optimism betrays them into thinking that their own energies suffice to win them complete, lasting, and gainful prosperity, or, finally, those who take refuge in an aggressively pessimistic outlook on life and maintain that their vices, weaknesses and moral ailments are inevitable, incurable, or perhaps even desirable as sure manifestations of personal freedom and sincerity. The Gospel of Christ recognizes the existence of human infirmities. It recognizes and denounces them with penetrating and often fierce sincerity. Yet it also understands them and cures them. It does not cherish the illusion that man is naturally good and self-sufficient, and needs only the ability to express himself as he pleases. Nor does it countenance a despairing acquiescence in the irremedial corruption of human nature. Christ's Gospel is light, newness, strength, salvation, and rebirth. It brings to birth a new and different kind of life, the marvels of which are proclaimed in the pages of the New Testament. Hence the admonition which St. Paul gives: "Do not be conformed to this world, but be reformed in the newness of your mind, that you may prove what is the good and the acceptable and the perfect will of God " (38)
Source: Ecclesiam Suam (Vatican.va)