19 The Church, whose work lies among men and operates through men, may see her divine mission obscured by human, too human, combination, persistently growing and developing like the cockle among the wheat of the Kingdom of God. Those who know the Savior's words on scandal and the giver of scandals, know, too, the judgment which the Church and all her sons must pronounce on what was and what is sin. But if, besides these reprehensible discrepancies be between faith and life, acts and words, exterior conduct and interior feelings, however numerous they be, anyone overlooks the overwhelming sum of authentic virtues, of spirit of sacrifice, fraternal love, heroic efforts of sanctity, he gives evidence of deplorable blindness and injustice. If later he forgets to apply the standard of severity, by which he measures the Church he hates, to other organizations in which he happens to be interested, then his appeal to an offended sense of purity identifies him with those who, for seeing the mote in their brother's eye, according to the Savior's incisive words, cannot see the beam in their own. But however suspicious the intention of those who make it their task, nay their vile profession, to scrutinize what is human in the Church, and although the priestly powers conferred by God are independent of the priest's human value, it yet remains true that at no moment of history, no individual, in no organization can dispense himself from the duty of loyally examining his conscience, of mercilessly purifying himself, and energetically renewing himself in spirit and in action. In Our Encyclical on the priesthood We have urged attention to the sacred duty of all those who belong to the Church, chiefly the members of the priestly and religious profession and of the lay apostolate, to square their faith and their conduct with the claims of the law of God and of the Church. And today we again repeat with all the insistency We can command: it is not enough to be a member of the Church of Christ, one needs to be a living member, in spirit and in truth, i.e., living in the state of grace and in the presence of God, either in innocence or in sincere repentance. If the Apostle of the nations, the vase of election, chastised his body and brought it into subjection: lest perhaps, when he had preached to others, he himself should become a castaway (1 Cor. ix. 27), could anybody responsible for the extension of the Kingdom of God claim any other method but personal sanctification? Only thus can we show to the present generation, and to the critics of the Church that "the salt of the earth," the leaven of Christianity has not decayed, but is ready to give the men of today - prisoners of doubt and error, victims of indifference, tired of their Faith and straying from God - the spiritual renewal they so much need. A Christianity which keeps a grip on itself, refuses every compromise with the world, takes the commands of God and the Church seriously, preserves its love of God and of men in all its freshness, such a Christianity can be, and will be, a model and a guide to a world which is sick to death and clamors for directions, unless it be condemned to a catastrophe that would baffle the imagination.
Source: Mit Brennender Sorge (Vatican.va)