The rivalry for religious converts and influence increases the lack of religious unity and the level of religious intolerance. This may cause conflict between Church and state. One religion may lose strength to another because it supported the losing political faction in a power struggle.
Missionary activity has traditionally been the cause of noticeable rivalries. In the 18th and 19th centuries the Christian missions fought against Hinduism in India, and in the 20th century Hindu missions fight against Christianity. Beginning with more traditional Hindu missions, this century has seen the emergence of a more entrepreneurial and extravagant style in the Transcendental Meditation, Hare Krishna and Divine Light organizations, with their hundreds of thousands of followers. Friction between the devotees of these cults and the Christian community has been high.
This rivalry is not only among world religions, but among denominations, sects and cults and between all these and non-religious ideologies.
In this matter, therefore, all Christians must compete in pious rivalry, and give constant proof of their concern for the spiritual well-being of other people by defending their Faith and teaching it to those who either do not know it at all, or do not know it well enough and therefore misjudge it. It is necessary that priests, families, and local apostolic organizations instill this religious duty in the young, from early childhood and adolescence, even in newly established Christian communities. Nor is there a dearth of favorable opportunities for stressing, in a suitable and effective manner, this duty of an apostolate: as for example, the preparation of children or newly baptized adults for the sacrament of Confirmation, through which "new strength is granted to the faithful courageously to guard and defend their Mother Church and the Faith they received from her." This preparation is especially suited for populations who have in their local customs special initiation rites, through which adolescents are officially received into their tribal groups. (Papal Encyclical, Princeps Pastorum, 28 November 1959).