26 Common participation in worship (communicatio in sacris) which harms the unity of the Church or involves formal acceptance of error or the danger of aberration in the faith, of scandal and indifferentism, is forbidden by divine law. On the other hand, pastoral experience shows clearly that, as regards our Eastern brethren, there should be taken into consideration the different cases of individuals, where neither the unity of the Church is hurt nor are verified the dangers that must be avoided, but where the needs of the salvation of souls and their spiritual good are impelling motives. For that reason the Catholic Church has always adopted and now adopts rather a mild policy, offering to all the means of salvation and an example of charity among Christians, through participation in the sacraments and in other sacred functions and things. With this in mind, "lest because of the harshness of our judgment we be an obstacle to those seeking salvation" and in order more and more to promote union with the Eastern Churches separated from us, the Sacred Council lays down the following policy.
Source: Orientalium Ecclesiarum (Vatican.va)