Christianity, from its beginning, has tended toward an intolerance that was rooted in the understanding of itself as revelation of the divine truth that became human in Jesus Christ himself. “I am the way, and the truth, and the life; no one comes to the Father, but by me” (John 14:6). To be a Christian is to “follow the truth” (3 John); the Christian proclamation is “the way of truth” (2 Peter 2:2). Those who do not acknowledge the truth are enemies “of the cross of Christ” (Philippians 3:18) who have “exchanged the truth about God for a lie” (Romans 1:25) and made themselves the advocates and confederates of the “adversary, the devil,” who “prowls around like a roaring lion” (1 Peter 5:8). Thus, one cannot make a deal with the Devil and his party—and in this lies the basis for parochialism in Christianity.

Christianity developed an intolerant attitude toward Judaism early in its history, especially after the destruction of the Temple of Jerusalem in 70 ce. This prejudice was rooted in the competition for religious converts and for possession of the Hebrew Scripture and its legacy. In order to proclaim itself as the “new Israel,” Christianity had to repudiate the claims of Israel’s traditional children. From the time of the composition of the Gospels, therefore, Jews were identified as the killers of Christ. Subsequent Christian theologians developed an elaborate picture of the Jews as the enemy of the faith, though some argued that the Jews must survive until the end of time as witness to the truth of Christian revelation. Such hostile and irrational views laid the foundation for centuries of anti-Semitism among Christians. Not until the 20th century was the negative depiction of the Jews in official teachings overturned in some churches.

Early Christianity, especially following the conversion of the emperor Constantine I, aimed at the elimination of paganism—the destruction of its institutions, temples, tradition, and the order of life based upon it. After Christianity’s victory over Greco-Roman religions, it left only the ruins of paganism still remaining. Christian missions of later centuries constantly aimed at the destruction of indigenous religions, including their cultic places and traditions (as in missions to the Anglo-Saxons, Germans, and Slavs). This objective was not realized in mission areas in which Christian political powers did not succeed in conquests—e.g., China and Japan—but in Indian Goa, for example, the temples and customs of all indigenous religions were eliminated by the Portuguese conquerors.

The attitude of intolerance was further reinforced when Islam confronted Christianity from the 7th century on. Islam understood itself as the conclusion and fulfillment of the Old and New Testament revelation. Christianity, however, understood Islam either as a new heresy (Muhammad, it was believed, was taught by a heretical or apostate monk) or eschatologically as the religion of the “false prophets” or of the Antichrist. The aggression of Christianity against Islam—on the Iberian Peninsula, in Palestine, and in the entire eastern Mediterranean area during the Crusades—was carried out under this fundamental attitude. Intolerance of indigenous religions was also manifested in Roman Catholic missions in the New World; in the Western Hemisphere, these missions resulted in the wholesale destruction of Native American cults and cultic places.

When the Reformation churches asserted the exclusive claim of possessing the Christian truth, they tried to carry it out with the help of the political and military power at their disposal. In the religious wars of the 16th and 17th centuries, Christian dogmatism developed into an internal fratricidal struggle in which each side sought to annihilate the other party in the name of truth. The fact that such attempts did not succeed led to new reflections upon the justification of claims to exclusive possession of absolute truth.

The intolerance of the Reformation territorial churches found its counterpart in the intolerance of the revolutionary groups of the Reformation period, such as that of the German radical reformer Thomas Müntzer, which wanted to force the coming of the kingdom of God through the dominion of the “elect” over the “godless.” Some see the ideology and techniques of many modern political revolutions and authoritarian regimes as either a legacy or a mimicking of old Christian patterns and methods.

Although calls for tolerance had been made earlier in church history, among the first to speak up consistently for tolerance were the Baptists and Spiritualists of the Reformation period. Their defense of tolerance contributed especially to the recognition of the evident contradiction between the theological self-conception of Christianity as a religion of love of God and neighbour and the inhumanity practiced by the churches in the persecution of dissenters. This recognition even provoked criticism of the Christian truths of faith themselves.

The Roman Catholic Church in the past consistently opposed the development of religious toleration and as late as the 20th century in some countries ensured that legal restrictions against Protestant minorities were established. With Pope John XXIII and the Second Vatican Council (1962–65), however, the church adopted a much more accommodating stance, which has been appropriate both to the ecumenical situation of Christendom since the late 20th century and to the personal character of the Christian faith.