After reciting the Angelus prayer June 19, the Pope had thousands of visitors in St. Peter's Square join him in praying a Hail Mary for "all of our Orthodox brothers and sisters."

Pope Francis noted that the day was Pentecost on the Julian calendar followed by the Orthodox. "Let us unite ourselves to the prayer of our Orthodox brothers and sisters, invoking the Holy Spirit so that it would assist with its gifts the patriarchs, archbishops and bishops gathered in the council."

The Pope's daily tweet repeated his message: "Let us join in prayer with our Orthodox brothers and sisters for the Holy and Great Council of the Orthodox Church opening today in Crete." Ecumenical Patriarch Bartholomew of Constantinople, who is presiding over the council meetings, retweeted the Pope's message.

In his homily at the Cathedral of St. Minas in Heraklion, Crete, Patriarch Bartholomew insisted the Orthodox Church is united in its faith in Christ and in church doctrine. "The Orthodox Church is one, but reveals itself in the world through its individual local vines, which are unbreakably and indivisibly attached to one -- to one church, to one body," he said.

The patriarch did not directly address the absence of delegations from the Orthodox churches of Bulgaria, Antioch, Georgia and Russia, which is the largest of the Orthodox churches. Although they had agreed in January to attend, the absent churches cited a variety of reasons for staying away, ranging from jurisdictional disputes to objections to the procedures adopted for the meeting. The patriarchs of the 10 participating churches had met separately June 17 and sent last-minute pleas to the four churches to attend.

In his homily, Patriarch Bartholomew said the Orthodox bishops need the council "so as to adopt the appropriate measures to protect the faithful from the prevailing errors" present in the world today. "The number of religious factions that are attempting to lead the Orthodox faithful astray are in the hundreds."

"Regardless of our different opinions, we Orthodox Christians ought to point out that the only road on our course in this world is unity," the patriarch said. "Of course, this road demands a living sacrifice, much work and is achieved after great struggle. It is certain that this council of ours will contribute toward this direction by creating a climate of mutual trust and understanding through our meeting in the Holy Spirit and through an edifying and sincere dialogue."

The unity of the Orthodox Church, he said, "does not take on the form of a federation, nor does it stem from congregating around some mortal figure. It proceeds from and is made complete by our common faith, which is synonymous with salvation, with eternal life."