From Dignitatis humanae, the Declaration on the Right of the Person and of Communities to Social and Civil Freedom in Religious Matters (1965):
13. Among the things that concern the good of the Church and indeed the welfare of society here on earth—things therefore that are always and everywhere to be kept secure and defended against all injury—this certainly is preeminent, namely, that the Church should enjoy that full measure of freedom which her care for the salvation of men requires. This is a sacred freedom, because the Only-begotten Son endowed with it the Church which He purchased with His blood. Indeed it is so much the property of the Church that to act against it is to act against the will of God. The freedom of the Church is the fundamental principle in what concerns the relations between the Church and governments and the whole civil order.
In human society and in the face of government the Church claims freedom for herself in her character as a spiritual authority, established by Christ the Lord, upon which there rests, by divine mandate, the duty of going out into the whole world and preaching the Gospel to every creature. The Church also claims freedom for herself in her character as a society of men who have the right to live in society in accordance with the precepts of the Christian faith.
In turn, where the principle of religious freedom is not only proclaimed in words or simply incorporated in law but also given sincere and practical application, there the Church succeeds in achieving a stable situation of right as well as of fact and the independence which is necessary for the fulfillment of her divine mission.
This independence is precisely what the authorities of the Church claim in society. At the same time, the Christian faithful, in common with all other men, possess the civil right not to be hindered in leading their lives in accordance with their consciences. Therefore, a harmony exists between the freedom of the Church and the religious freedom which is to be recognized as the right of all men and communities and sanctioned by constitutional law.
14. In order to be faithful to the divine command, “teach all nations” (Matt. 28:19-20), the Catholic Church must work with all urgency and concern “that the word of God be spread abroad and glorified” (2 Thess. 3:1). Hence the Church earnestly begs of its children that, “first of all, supplications, prayers, petitions, acts of thanksgiving be made for all men. … For this is good and agreeable in the sight of God our Savior, who wills that all men be saved and come to the knowledge of the truth” (1 Tim. 2:1-4). In the formation of their consciences, the Christian faithful ought carefully to attend to the sacred and certain doctrine of the Church. For the Church is, by the will of Christ, the teacher of the truth. It is her duty to give utterance to, and authoritatively to teach, that truth which is Christ Himself, and also to declare and confirm by her authority those principles of the moral order which have their origins in human nature itself. Furthermore, let Christians walk in wisdom in the face of those outside, “in the Holy Spirit, in unaffected love, in the word of truth” (2 Cor. 6:6-7), and let them be about their task of spreading the light of life with all confidence and apostolic courage, even to the shedding of their blood.
The disciple is bound by a grave obligation toward Christ, his Master, ever more fully to understand the truth received from Him, faithfully to proclaim it, and vigorously to defend it, never—be it understood—having recourse to means that are incompatible with the spirit of the Gospel. At the same time, the charity of Christ urges him to love and have prudence and patience in his dealings with those who are in error or in ignorance with regard to the faith. All is to be taken into account—the Christian duty to Christ, the life-giving word which must be proclaimed, the rights of the human person, and the measure of grace granted by God through Christ to men who are invited freely to accept and profess the faith.
 Cf. Leo XIII, letter Officio Sanctissimo, Dec. 22, 1887: AAS 20 (1887), p. 269; idem, letter Ex Litteris, April 7, 1887: AAS 19 (1886), p. 465.
 Cf. Mark 16:15; Matt. 28:18-20, Pius XII, encycl. Summi Pontificatus, Oct. 20, 1939: AAS 31 (1939), pp. 445–46.
 Cf. Pius XI, letter Firmissimam Constantiam, March 28, 1937: AAS 29 (1937), p. 196.
 Cf. Pius XII, allocution, Ci Riesce, Dec. 6, 1953: AAS 45 (1953), p. 802.
 Cf. Pius XII, radio message, March 23, 1952: AAS 44 (1952) pp. 270–78.
 Cf. Acts 4:29.
 Cf. John XXIII, encycl. Pacem in Terris, April 11, 1963: AAS 55 (1963), pp. 299–300.