Jesus Christ taught with absolute clarity that we should worship the One True God and he never joined in prayer with anyone from a different religion nor encouraged his disciples to do so. Faithful Christ’s example and command, the Church has continually taught that we should avoid all forms of false worship and superstition, and can never encourage others to offer prayers within a religion not founded by God Himself.
During his forty days of temptation in the wilderness, Christ was tempted by the devil, who said show him the world and said, “If you worship me, it will all be yours” (Lk 4:7). In response, Jesus rejected false worship and worldly power, saying, “It is written, ‘You shall worship the Lord your God, and him only shall you serve’” (Lk 4:8). He was well aware of the precept, “Do not follow other gods, the gods of the peoples around you” (Dt 6:14). In order to preserve the purity of Catholic faith, and the holiness of worship offered to Holy Trinity, St. Paul admonished the early Church, “Do not be unequally yoked together with unbelievers: for what fellowship has righteousness with unrighteousness? Or what communion has light with darkness? What accord has Christ with Belial? Or what has a believer in common with an unbeliever?” (2 Cor 6:14-15). In continuity with all divine revelation, St. Paul then concluded by repeating the strict command of God Himself, given through the prophet Isaiah to those who had mingled with idolaters: “Therefore come out from them, and be separate from them, says the Lord” (2 Cor 6:17; Is 52:11).
Sometimes a distinction is made between inter-religious prayer and multi-religious prayer. Undoubtedly, as seen above, Christians may not pray with those of other religions in inter-religious prayer. Cardinal Ratzinger noted that for Christians and other religions, “their way of understanding the divinity and, therefore, their way of addressing it, is so different that a common prayer would be a fiction, it would not be true.” But may licitly pray alongside those of other religions in multi-religious prayer? By no means. Pope Pius XI, in his encyclical Mortalium Animos (1928) clearly condemned these sorts of meetings, saying:Certainly such attempts can nowise be approved by Catholics, founded as they are on that false opinion which considers all religions to be more or less good and praiseworthy. […] Not only are those who hold this opinion in error and deceived, but also in distorting the idea of true religion they reject it.
The result is that, little by little, those who engage in “multi-religious” prayer meetings end up abandoning the truth that God has become incarnate in Jesus Christ alone, and through Christ given a single, definitive, divine revelation of Himself. The result of participating in inter-religious prayer meetings would be indifferentism toward the Catholic faith, as well as an increased relativism with respect to truth itself.
It is good for Catholics to pray for a good intention, such as peace or preservation from plague. However, as Pius XII stated, “we must not for its sake neglect the virtue of loyalty in Christ” (Orientalis Ecclesiae, 16). Catholics may not regard the propagation of any non-Catholic religion as good and praiseworthy in itself, nor may we directly encourage or promote the religious activities of any non-Catholic group. This is because, as St. Paul stated, “what pagans sacrifice they offer to demons and not to God” (1 Cor 10:20). The Apostle to the Gentiles stated very clearly to the early Christians and to the Church of all times, “I do not want you to be partners with demons.” Therefore, Christians should avoid praying with non-Christians or alongside them. Instead, we should pray for non-Christians and encourage them to worship the One True God, saying with prophet Elijah, “If the LORD is God, follow him; but if Baal, then follow him” (1 Kings 18:21).
That we Catholics can pray and adore with the non-Christians the one God is not true. We don’t pray and adore with them. In the act of prayer, we Christians always adore the Holy Trinity, we don’t simply adore “the one God” but the Holy Trinity consciously—Father, Son, and Holy Ghost. The non-Christians reject the Holy Trinity. When non-Christians pray, they do not pray on the supernatural level of faith. Their prayer is essentially different. Precisely because we turn to God and adore Him as children constituted in the ineffable dignity of divine filial adoption, and we do this with supernatural faith. However, the non-Christians do not have supernatural faith.
The subjective act of prayer of non-Christians is also different from the Christian act of prayer because their understanding of God is different from ours. We should bear in mind the fact that non-Christians, accepting propositions asserted of God that are not of divine origin, are in danger of offering a false worship to God even on the natural level, because they have a wrongheaded idea of God itself.
We must always keep in mind that non-Christian religions and the Catholic faith are not on the same level. For a believing Catholic, non-Christian religions are not the true religion; the Catholic faith is the only true religion, which God positively wills as He declared it in His Divine Son Jesus Christ.
Conclusion:
To pray alongside someone who is praying to a false god is still a sin against the One True God. Our prayers are not like lines that all reach the same center. Rather, the shape of all prayer must be in the shape of the Cross. To choose to be a part of a “multi-prayer” service in which false prayer is offered, is to at least commit proximate material cooperation in evil. It also gives grave scandal not only to Catholics, but to the ones performing the false prayer because one’s presence at such a meeting implicitly accepts their prayers as something not contrary to good morals.