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.
Source: Dignitatis Humanae (Vatican.va)