Pope Leo XIV has taken as his motto “In Illo uno unum”: In the one Christ we are one. Last November he joined Ecumenical Patriarch Bartholomew of Constantinople, Patriarch Theodore II of Alexandria and other Orthodox representatives to mark the 1,700th anniversary of the First Council of Nicaea. The pope and the ecumenical patriarch affirmed in a joint declaration their churches’ orientation toward “the hoped-for restoration of full communion.” Even Patriarch Kirill of Moscow, who leads one of the Orthodox churches most skeptical about Rome, has expressed hope that relations “will progressively develop for a joint witness to Christ.”
These symbolic gestures don’t directly address the longstanding theological barriers, but there has been some progress over the past several years. The 2023 Alexandria Document was an important step toward a joint understanding of papal authority, though not all Orthodox churches ratified the statement.
Patriarch Bartholomew, for his part, has prayed that the obstacles of the filioque—Rome’s teaching that the Holy Spirit proceeds from the Father and the Son, rather than from the Father alone—and papal infallibility be resolved so that they “no longer serve as stumbling blocks to the communion of our churches.” The patriarch mentioned these two obstacles intentionally, and a joint international commission plans to examine them head-on over the next several years.
But reunion is the work of all believers, not just hierarchs and theologians.
