ROME — Pope Francis opened 2015 on Thursday by calling on the world to redouble its efforts for peace, saying “peace is always possible, and we have to seek it,” and also by asking Catholics to remain loyal to their Church.

“May there never again be wars, but always the desire and commitment to peace and fraternity among peoples,” the pope said in his traditional noontime Angelus address on New Year’s Day, delivered before a crowd of more than 100,000 gathered in St. Peter’s Square.

“Prayer is at the root of peace,” Francis said.

Screens in St. Peter’s Square showed the playing of a famous Italian bell in the northern city of Rovereto, one of the largest bells in the world, which was originally erected to commemorate Italy’s fallen in World War I and is today considered a shrine to peace.

The pope’s New Year’s message built on his Christmas Day Urbi et Orbi address, in which Francis called for great attention to resolving conflicts from the Middle East to Ukraine and Africa.

It also came on a day, Jan. 1, that’s been set aside since 1968 at the direction of Pope Paul VI as a “World Day of Peace,” which Francis devoted this year to the fight against human trafficking and slavery.

The push for peace has been a keen emphasis for Francis during the past year.

In June, he staged a surprise peace prayer with the Israeli and Palestinian presidents in the Vatican gardens. He repeatedly denounced violence in Iraq and Syria fueled by ISIS forces, and in December he played a pivotal role in brokering a deal for the restoration of relations between the United States and Cuba.

Earlier on New Year’s morning, Pope Francis delivered a homily during a Mass devoted to the Virgin Mary in which he delivered a strong call to Catholics to remain loyal to the Church.

Without the Church, Francis said, “our relationship with Christ would be at the mercy of our imagination, our interpretation, [and] our moods.”

At one point, Francis added the word “hierarchical” to modify “Church” in his text, making it clear he meant the visible, institutional Church.

“To separate Jesus from the Church would introduce an ‘absurd dichotomy’,” Francis said, quoting Pope Paul VI, adding the rest of the citation: It is not possible “to love Christ but without the Church, to listen to Christ but not the Church, to belong to Christ but outside the Church.”

“No manifestation of Christ, even the most mystical, can ever be detached from the flesh and blood of the Church, from the historical concreteness of the Body of Christ,” the pope said, reprising a theme that was also a central concern of his predecessor, Pope Benedict XVI.

“Without the Church, Jesus Christ ends up as an idea, a moral teaching, a feeling,” Francis said, calling Christ and the Church “inseparable.”

The comments came toward the end of a holiday season that began with Pope Francis delivering a stinging indictment of the upper echelons of the Vatican for being infected with 15 spiritual illnesses, including the “terrorism of gossip” and “spiritual Alzheimer’s.”

In context, the pontiff’s message in the homily seemed to be that whatever the occasional failures of the Church’s leadership, that’s no excuse for cutting it loose or giving up on it.

On the Catholic calendar, Jan. 1 is a feast dedicated to Mary as the Mother of God, which has keen personal significance for Francis.

In Latin America, the future pope saw the diverse Marian feasts observed by the countries and ethnic groups of the continent as a pillar of popular culture, often making a point of celebrating these feasts himself.

As a student in Germany, the future pope also became familiar with a famous 18th-century painting titled “Mary, Untier of Knots,” based on the idea that while Eve tied humanity in knots through her disobedience to God in the Garden of Eden, Mary untied those knots by accepting God’s will that she give birth to Jesus.

When Francis traveled to Brazil in July 2013 to lead the Church’s World Youth Day celebrations, he asked that an additional day be added to his schedule so that he could visit the shrine of Our Lady of Aparecida, one of the most popular Marian sanctuaries in Latin America, where he consecrated his papacy to Mary.

In his homily on Thursday, Francis said that “Jesus cannot be understood without his mother.”

At one point, the pope also introduced an impromptu Marian devotion, inviting the assembly in St. Peter’s Basilica to rise, face a statue of Mary, and repeat three times, “Mary, Mother of God.”

The pope recalled that at the 5th-century Council of Ephesus, a crowd actually shouted that phrase at the gathered bishops while waving clubs at them, threatening violence if they didn’t formally proclaim Mary as the Mother of God.

This time, Francis jokingly invited people to make the chant “without clubs.”

He led the crowd in St. Peter’s Square in the same chant during his Angelus address.

“No other creature has ever seen God’s face shine upon it as did Mary,” the pope said in his earlier homily. “She gave a human face to the eternal Word, so that all of us can contemplate him.”

“She, the Mother of God, is also the Mother of the Church, and through the Church, the mother of all men and women and of every people,” he said.

Both devotion to Mary and the centrality of the Church are hallmarks of Catholic tradition that set it apart from other Christian denominations, and have sometimes been bones of contention in Catholicism’s relationships with other branches of Christianity.

Although outreach to other Christian churches has been a hallmark of Francis’ papacy — including a trip in July to visit a Pentecostal church in Caserta, Italy, led by a friend of the pope’s from Argentina — his remarks Thursday suggest he doesn’t want that engagement to come at the expense of traditional pillars of Catholic identity.

Francis’ next public appearance is set for his noontime Angelus address on Sunday. On Tuesday, he’ll lead the traditional Mass for the feast of the Epiphany.

On Jan. 12, Francis will deliver his annual address to the diplomatic corps, generally the pope’s most important foreign policy speech of the year, before departing later that day for a week-long trip to Sri Lanka and the Philippines.