The Vatican, citing local organizers, estimated 12,000 people attended the open-air Mass on Sunday afternoon in the capital of Sofia or watched it on giant TV screens in a nearby square. Catholics account for less than 1% of Bulgaria's population of 7 million.
In his homily, Francis told the faithful God's love inspires all to work for the common good. He said: "This love enables us to serve the poor and to become protagonists of the revolution of charity and service, capable of resisting the pathologies of consumeristic and superficial individualism."
Francis is scheduled to travel Monday to the Catholic stronghold in Rakovsky to celebrate 200 children receiving the sacrament of first communion.
Pope Francis is seeking to build new paths of dialogue with the Bulgarian Orthodox Church, noting Christianity's shared history of martyrdom and mission.
Francis met Sunday with Patriarch Neofit at the headquarters of the Holy Synod, the Bulgarian church's governing body, before praying alone in the Orthodox cathedral.
Relations between the two churches are cordial but hardly warm. The Holy Synod doesn't participate in official Vatican-Orthodox theological dialogue, and made clear that it wouldn't take part in any joint services or prayers with Francis.
Francis referred to the "wounds" of division caused by the 1,000-year-old schism that divided Christianity and said he was "confident with the help of God, and in his good time, these contacts will have a positive effect on many other dimensions of our dialogue."
Neofit, however, was clear that he felt the Bulgarian Church would remain the keepers of true Christianity.
Pope Francis is urging Bulgarians to open their hearts and homes to migrants, arguing that a country like Bulgaria, which is losing its population to emigration, should well understand the forces that drive people to leave their native lands.
As he arrived Sunday in the Balkan nation, Francis "respectfully suggested" Bulgaria recognize that migrants coming to their country are fleeing war, conflict and dire poverty to find safety and opportunity.
He appealed to government authorities "that you not close your eyes, your hearts or your hands — in accordance with your best tradition — to those who knock at your door."
Bulgaria's center-right, pro-Brussels coalition government has called for the European Union to close its borders to migrants and has sealed off its own border to Turkey with a barbed-wire fence.
Human rights organizations and the European Commission have accused Bulgaria of violating EU asylum laws.
Bulgarian Prime Minister Boyko Borisov has offered Pope Francis a very personal gift at the start of his visit to the Balkan nation: A cup of Bulgarian yogurt.
Borisov said Sunday after meeting with Francis upon his arrival in Sofia that on previous occasions he had been told by Francis that the first time he had heard about Bulgaria was during his childhood in Argentina when his grandmother gave him Bulgarian yogurt.
Borisov gave Francis the yogurt when they met at the airport. The official gifts also included an Orthodox icon and a traditional episcopal vestment.
The prime minister said: "I was happy to welcome a man who is the symbol of faith in our world. Pope Francis' prayers for peace are extremely important for our region that stretches from Ukraine to the east to the Western Balkans."
Pope Francis has arrived in Bulgaria, the European Union's poorest country and one that taken a hard line against migrants.
That stance conflicts with the pontiff's view that reaching out to vulnerable people is a moral imperative.
On a two-day trip that began Sunday, Francis plans to tour a refugee center and dive into the Vatican's complicated relations with the Bulgarian Orthodox Church.
Later in the day, Francis is meeting with Prime Minister Boyko Borisov, whose center-right, pro-Brussels coalition government includes three nationalist, anti-migrant parties. The government has called for the closure of EU borders to migrants and sealed off its own frontier to Turkey with a barbed-wire fence.
Bulgaria, which joined the EU in 2007, is the bloc's poorest country, with the lowest average monthly salary — 575 euros ($645) — and the smallest average monthly pension of 190 euros ($213).
Pope Francis is heading to Bulgaria, the European Union's poorest country and one that taken a hard line against migrants, which conflicts with the pontiff's view that reaching out to vulnerable people is a moral imperative.
Francis is expected to visit a refugee center during his two-day visit starting Sunday, as well as dive into the Vatican's complicated relations with the Bulgarian Orthodox Church. The trip ends with a daylong stop Tuesday in neighboring North Macedonia, the first by a pope.
Francis starts his Bulgarian trip by meeting with Prime Minister Boyko Borisov, whose center-right, pro-Brussels coalition government includes three nationalist, anti-migrant parties. The government has called for the closure of EU borders to migrants and sealed off its own frontier to Turkey with a barbed-wire fence.
The Argentine pope has made the plight of migrants and refugees a hallmark of his papacy. His visit falls just three weeks before European Parliament elections across the EU's 28 nations in which nationalist, anti-migrant parties are expected to make a solid showing.