Gaudium et Spes §21

²¹ In her loyal devotion to God and men, the Church has already repudiated and cannot cease repudiating, sorrowfully but as firmly as possible, those poisonous doctrines and actions which contradict reason and the common experience of humanity, and dethrone man from his native excellence. Still, she strives to detect in the atheistic mind the hidden causes for the denial of God; conscious of how weighty are the questions which atheism raises, and motivated by love for all men, she believes these questions ought to be examined seriously and more profoundly. The Church holds that the recognition of God is in no way hostile to man's dignity, since this dignity is rooted and perfected in God. For man was made an intelligent and free member of society by God Who created him, but even more important, he is called as a son to commune with God and share in His happiness. She further teaches that a hope related to the end of time does not diminish the importance of intervening duties but rather undergirds the acquittal of them with fresh incentives. By contrast, when a divine instruction and the hope of life eternal are wanting, man's dignity is most grievously lacerated, as current events often attest; riddles of life and death, of guilt and of grief go unsolved with the frequent result that men succumb to despair. Meanwhile every man remains to himself an unsolved puzzle, however obscurely he may perceive it. For on certain occasions no one can entirely escape the kind of self-questioning mentioned earlier, especially when life's major events take place. To this questioning only God fully and most certainly provides an answer as He summons man to higher knowledge and humbler probing. The remedy which must be applied to atheism, however, is to be sought in a proper presentation of the Church's teaching as well as in the integral life of the Church and her members. For it is the function of the Church, led by the Holy Spirit Who renews and purifies her ceaselessly, to make God the Father and His Incarnate Son present and in a sense visible. This result is achieved chiefly by the witness of a living and mature faith, namely, one trained to see difficulties clearly and to master them. Many martyrs have given luminous witness to this faith and continue to do so. This faith needs to prove its fruitfulness by penetrating the believer's entire life, including its worldly dimensions, and by activating him toward justice and love, especially regarding the needy. What does the most reveal God's presence, however, is the brotherly charity of the faithful who are united in spirit as they work together for the faith of the Gospel and who prove themselves a sign of unity. While rejecting atheism, root and branch, the Church sincerely professes that all men, believers and unbelievers alike, ought to work for the rightful betterment of this world in which all alike live; such an ideal cannot be realized, however, apart from sincere and prudent dialogue. Hence the Church protests against the distinction which some state authorities make between believers and unbelievers, with prejudice to the fundamental rights of the human person. The Church calls for the active liberty of believers to build up in this world God's temple too. She courteously invites atheists to examine the Gospel of Christ with an open mind. Above all the Church knows that her message is in harmony with the most secret desires of the human heart when she champions the dignity of the human vocation, restoring hope to those who have already despaired of anything higher than their present lot. Far from diminishing man, her message brings to his development light, life and freedom. Apart from this message nothing will avail to fill up the heart of man: "Thou hast made us for Thyself," O Lord, "and our hearts are restless till they rest in Thee."