Christianity is a religion frayed over the centuries into many denominations . On Sunday , Pope Francis and the head of a major one vowed to heal one of the church 's oldest splits . The Great Schism of 1054 separated the Catholic and Eastern Orthodox churches . Both profess similar doctrine and worship in similar ways , but a millennium ago , Eastern Orthodoxy rejected the ultimate authority of the Pope . Francis and Patriarch Bartholomew I -- the spiritual leader of some 300 million Orthodox Christians worldwide -- signed a declaration on Sunday committing to unity between the two churches . Together , they celebrated a divine liturgy at the Patriarchal Church of St. George in Istanbul on Francis ' last day in the predominantly Muslim nation -- his first trip there . Somber intonations and hymns reverberated through the church as the two spiritual leaders prayed and offered reflections and Francis tried to allay worries . Unity , not submission . Neither church will submit to nor assimilate the other , the Pope said in his homily , but they will work `` towards the restoration of full Communion . '' `` I want to assure each one of you here that , to reach the desired goal of full unity , the Catholic Church does not intend to impose any conditions except that of the shared profession of faith , '' Francis said . He was at St. George 's at the Patriarch 's invitation , which he extended shortly after Francis ' inauguration . Sunday 's celebrations marked the feast of St. Andrew , the founder of the Eastern Church . He was also the older brother of St. Peter , the founding father of the Catholic Church . 'Blood of martyrdom ' In his part of the call for unity , the Orthodox leader alluded to attacks by radical Islamists on Christians . `` We no longer have the luxury of isolated action , '' Bartholomew said . `` The modern persecutors of Christians do not ask which church their victims belong to . The unity that concerns us is regrettably already occurring in certain regions of the world through the blood of martyrdom . '' Over the past decade , first al Qaeda and then ISIS have forced Christians to flee Iraq and Syria . Far fewer Christians remain in areas under ISIS control . Some rely on their faith in God ; others pay terrorists a protection tax . Growing numbers , especially from Syria , have ended up in Turkey.The nation is reeling from the influx of around 1.5 million Syrian refugees , the vast majority Muslim . Religion is also splitting Turkey . Opponents fear its conservative government will weaken the secular identity of the post-Ottoman Empire . Instability rages at its border , with ISIS and its leader , Abu Bakr al-Baghdadi , announcing their intention to take over large swaths of territory for their self-proclaimed Islamic State . Fourth pope in Turkey . Francis is the fourth pope to travel to Turkey , following in the footsteps of Paul VI , John Paul II and Benedict XVI . The Pope was also expected to meet with young people from the Salesian community from Turkey , the Middle East and Africa before heading to the airport later Sunday . Salesians , the second largest Catholic order , help orphans and at-risk children , according to their website . On Friday , the first day of his visit , Francis called for religious tolerance and dialogue to counter extremism in the Middle East , as he met with Turkey 's leaders . `` Fanaticism and fundamentalism , as well as irrational fears , which foster misunderstanding and discrimination , need to be countered by the solidarity of all believers , '' he said . The world is morally obligated to help Turkey care for the great number of refugees it has taken in , Francis said . Erdogan criticizes Islamophobia . In an address given in Francis ' presence , Turkish President Recep Tayyip Erdogan highlighted what he said was a disturbing trend of increased racism and Islamophobia in the West , while Islamist extremism wracks parts of the Middle East . The world must come together if it wants to combat terrorism , he said . The Turkish leader also suggested the West should not turn a blind eye to abuses committed by Syrian President Bashar al-Assad while it pursues ISIS . The timing of the Pope 's visit , in this period of unrest , is extremely significant , Erdogan added , voicing hope that it would lead to an `` auspicious era '' of improved relations in the world .
Pope Francis pushes for reunification with Orthodox Christians . Pontiff to meet with youths before departing . During visit , Francis calls for religious freedom and tolerance to counter extremism . Comment: Fanaticism and fundamentalism need to be countered by those of faith .