Moreover, if by “active participation” in Protestant services, one gives “countenance to a false Christianity” which means the appearance of approval to doctrines and practices contrary to the Catholic faith, then such active participation in this sense is prohibited. In such instances, we act contrary to our faith which we are obliged to profess always, in our words and deeds. The Catholic profession of faith is fundamentally different than Protestant ecclesiology, epistemology, and with regard to many theological doctrines and liturgical practices. We must always avoid countenance to Protestant beliefs and practices which are contary to Catholicism.
Catholics can, however, in certain situations “observe” Protestant services for educational and ecumenical purposes to deepen one’s understanding of that particular ecclesial community, and to foster all that can lead to unity and harmony, all the while being careful not to give even the appearance of approval of a false Christianity. So, one must act prudently, weighing the ecumenical value against the risk of giving countenance to a false Christianity.
Pius XI’s words are not contrary to ecumenism, but rather protect the Church from a false or misguided ecumenism which confuses the identity, purpose, and mission of the Catholic Church which possesses the fullness of truth and communion with Jesus Christ with something less.