Dublin, Ireland (CNN) Hundreds of thousands of people braved wet and windy weather to attend Pope Francis' Mass at Phoenix Park in Dublin on Sunday, while thousands more gathered in the city center for protests against clerical sexual abuse amid fresh reports the Pontiff ignored allegations stretching back years.

"We ask forgiveness for the abuses in Ireland," said Pope Francis at the Mass, listing a litany of abuses including clerical sex crimes, a lack of compassion and action by church leaders and the separation of single mothers and children in industrial laundries.

"We ask forgiveness for all the times that we, as the church, did not provide survivors of any kind of abuse compassion, to look for justice, and the truth, and concrete actions, so we ask forgiveness," Pope Francis said at the Mass, which was expected to attract over 500,000 people and concludes his two-day visit to Ireland.

An aerial view of the crowd at Phoenix Park in Dublin as Pope Francis attends the closing Mass at the World Meeting of Families, as part of his visit to Ireland.

The visit coincides with the World Meeting of Families, a gathering of the Catholic Church that was thrown into chaos last week by a Pennsylvania grand jury report detailing decades of sexual abuse and cover-ups by clerics.

On Sunday, Pope Francis faced calls for his resignation from the former Vatican ambassador to Washington, Carlo Maria Vigano, who said in a letter that he told the Pontiff about allegations of sexual abuse against the prominent Cardinal Theodore McCarrick back in 2013. Vigano said the Pontiff did nothing about it

A source close to Vigano confirmed the letter is genuine.

Speaking to the press Sunday on his flight back to Italy from Ireland, Pope Francis said, "I will not say a single word on this." He added that after some time passes, "I may speak."

The Pope told reporters he believes the statement from Vigano speaks for itself. "I read the statement this morning, and I must tell you sincerely ... read the statement carefully and make your own judgment," the Pope said.

McCarrick, 88, who once led the Archdiocese of Washington and was a force in American politics, resigned last month after a decades-old allegation of sexual abuse of a teenage altar boy.

Protesters assemble at the General Post Office in Dublin, ahead of Pope Francis' Sunday Mass.

Earlier in the day, the Pontiff begged "the Lord's forgiveness" for clerical sexual abuse, during a visit to the Knock Sanctuary, a Catholic pilgrimage site where villagers say they witnessed an apparition of the Virgin Mary in 1879.

"None of us can fail to be moved by the stories of minors who suffered abuse, were robbed of their innocence and left scarred by painful memories," Francis said during a speech at the Sanctuary.

As thousands of people filled Phoenix Park for Sunday Mass, large crowds also gathered in Dublin City center for a "Stand for Truth" solidarity event, organized by Colm O'Gorman, an abuse survivor who is now executive director of Amnesty International.

Big crowds at the "Stand for Truth" solidarity event, organized by Colm O'Gorman, an abuse survivor who is now executive director of Amnesty International. pic.twitter.com/IaedYifZjg — Eliza Mackintosh (@elizamackintosh) August 26, 2018

The Pope again apologized for the "appalling" historic child abuse in the Church on Saturday after Irish Prime Minister Leo Varadkar called for "zero tolerance" against predator priests and to ensure "that from words flow actions."

Varadkar, the country's first openly gay leader, said the time had come "for us to build a new, more mature relationship between church and state in Ireland -- a new covenant for the 21st century."

Photos: In pictures: Pope Francis visits Ireland Pope Francis arrives at the closing Mass of his Ireland visit at Phoenix Park in Dublin, Ireland on Sunday, August 26, 2018. Hide Caption 1 of 23 Photos: In pictures: Pope Francis visits Ireland Clerical sex abuse protesters assemble at the General Post Office in Dublin before marching to the Garden of Remembrance during the Pope's visit to Ireland on Sunday. Hide Caption 2 of 23 Photos: In pictures: Pope Francis visits Ireland Pope Francis celebrates Mass at Phoenix Park in Dublin, Ireland, on Sunday. Hide Caption 3 of 23 Photos: In pictures: Pope Francis visits Ireland An aerial view of the crowd at Phoenix Park in Dublin as Pope Francis celebrates the closing Mass at the World Meeting of Families on Sunday. Hide Caption 4 of 23 Photos: In pictures: Pope Francis visits Ireland An aide adjusts Pope Francis' cape as he speaks at the Knock Shrine in Knock, Ireland, on Sunday. Hide Caption 5 of 23 Photos: In pictures: Pope Francis visits Ireland People wait for the arrival of Pope Francis in front of the Knock Shrine on Sunday. Hide Caption 6 of 23 Photos: In pictures: Pope Francis visits Ireland Pope Francis passes by a banner of a protester as he leaves St. Mary's Pro-Cathedral in Dublin on Saturday. The Pope spoke of his shame over the "appalling crimes" of historic child abuse in the Catholic Church and said outrage was justified. However, he failed to specifically mention the current scandal over a US grand jury report documenting at least 1,000 cases of clerical pedophilia. Hide Caption 7 of 23 Photos: In pictures: Pope Francis visits Ireland Pope Francis prays at St. Mary's Pro-Cathedral in Dublin on Saturday. Hide Caption 8 of 23 Photos: In pictures: Pope Francis visits Ireland Pope Francis waves to the waiting crowds on College Green in Dublin on Saturday. Hide Caption 9 of 23 Photos: In pictures: Pope Francis visits Ireland Nuns wait for Pope Francis to arrive for the Festival of Families on Saturday. Hide Caption 10 of 23 Photos: In pictures: Pope Francis visits Ireland Pope Francis leaves St. Mary's Pro-Cathedral in Dublin after meeting recently married couples, and couples preparing for the Sacrament of Marriage, as part of his visit to Ireland. Hide Caption 11 of 23 Photos: In pictures: Pope Francis visits Ireland Riverdance performs at the Festival of Families. Hide Caption 12 of 23 Photos: In pictures: Pope Francis visits Ireland Speaking in a hall in Dublin Castle on Saturday, Pope Francis addresses the sexual abuse scandal within the Catholic Church, saying, "the failure of ecclesiastical authorities -- bishops, religious superiors, priests and others -- adequately to address these appalling crimes has rightly given rise to outrage, and remains a source of pain and shame for the Catholic community. I myself share those sentiments." Hide Caption 13 of 23 Photos: In pictures: Pope Francis visits Ireland A journalist reacts inside the media center as Pope Francis arrives at Dublin Airport on Saturday. Hide Caption 14 of 23 Photos: In pictures: Pope Francis visits Ireland The Pope disembarks from the aircraft as he arrives in Dublin on Saturday. Hide Caption 15 of 23 Photos: In pictures: Pope Francis visits Ireland Priests await the arrival of Pope Francis at St. Mary's Pro-Cathedral. Hide Caption 16 of 23 Photos: In pictures: Pope Francis visits Ireland Protesters tie baby shoes to a post, signifying the children who died in mother and baby homes in Ireland, during a protest in Dublin ahead of the start of the Pope's visit to Ireland. Hide Caption 17 of 23 Photos: In pictures: Pope Francis visits Ireland The Pope is greeted by Archbishop Eamon Martin as he arrives at Dublin Airport on Saturday. Hide Caption 18 of 23 Photos: In pictures: Pope Francis visits Ireland Pope Francis is flanked by Irish President Michael Higgins upon his arrival at the presidential residence in Dublin on Saturday. Hide Caption 19 of 23 Photos: In pictures: Pope Francis visits Ireland Members of the armed forces arrive before the meeting between the Pope and Irish President Michael Higgins at Aras an Uachtarain on Saturday. Hide Caption 20 of 23 Photos: In pictures: Pope Francis visits Ireland A crowd reacts to Pope Francis' arrival for the Festival of Families. Hide Caption 21 of 23 Photos: In pictures: Pope Francis visits Ireland Pope Francis waves to the crowd at Dublin Airport on Saturday. Hide Caption 22 of 23 Photos: In pictures: Pope Francis visits Ireland Rainbow flags and blue ribbons are tied to Ha'penny Bridge in Dublin to remember the victims of Catholic Church clerical sex abuse. Hide Caption 23 of 23

It's a very different reception -- and a very different Ireland -- to the last papal visit in 1979, when Pope John Paul II was greeted like a rock star in Phoenix Park by nearly one-third of the country's population.

"The church's hold on public life in Ireland has fundamentally changed since '79," John Allen, who has written multiple books on the Vatican, told CNN.

In the nearly four decades that have elapsed, Ireland has become a far less Catholic country both socially and legally. Irish voters have struck down bans on divorce, same-sex marriage and, most recently, abortion. And Ireland's church attendance has waned from 90% to about 30% as revelations of abuse by Catholic-run institutions continue to damage its moral authority and diminish its influence.

Catholic Ireland at a crossroad?

More than 10,000 people also joined the Facebook event "Say Nope to the Pope," a campaign calling on protesters to snap up tickets to Mass and then not show up. Another 9,000 signed up for a "Stand for Truth" solidarity event. And as the Pope addresses the faithful at 3 p.m., a silent vigil was set to take p place in the town of Tuam, where 800 children's bodies were discovered last year at a former Catholic church mother-and-baby home.

Some local leaders boycotted a formal reception with the Pope, too. Orla O'Connor, director of the National Women's Council of Ireland, said she declined an invitation to join the Pope and representatives of civil society on Saturday in protest over the "trauma" that the Church has caused women, especially in blocking rights and equality.

"Say Nope to the Pope," a campaign calling on protesters to snap up tickets to mass and then not show up, is underway outside the General Post Office in Dublin. pic.twitter.com/MysMo9G1gB — Eliza Mackintosh (@elizamackintosh) August 26, 2018

But even so, Ireland remains a country where 78% of men and women still check the "Catholic" box. All tickets were swept up to see Pope Francis on Sunday at the Shrine of Our Lady of Knock in County Mayo.

"It's something of a paradox. We're at a stage where we consider ourselves a post-Catholic society, but people can't stop talking about Catholicism," Eamon Maher, co-editor of "Tracing the Cultural Legacy of Irish Catholicism," told CNN. "It's still a defining feature of what makes the Irish, Irish."

Two American cardinals dropped out of the World Meeting of Families as a result of the report, including Cardinal Donald Wuerl, the former Bishop of Pittsburgh and a key papal ally. Weurl, who was accused of helping to cover up abusive behavior, was to deliver the keynote address on "the welfare of the family." In the wake of the report, the bishop said he "did everything that I possibly could" to stop abuse from happening.

In response to rising anger over the revelations, the Pope issued a letter on Monday acknowledging the church's failure to act over abuse, but the apology has been criticized by victims -- as well as Irish clergy members -- for not going far enough.

And after the Archbishop of Dublin, Diarmuid Martin, sparked outrage earlier this month when he indicated that time would be "very tight" for the Pope to meet with abuse survivors on his two-day visit, the Vatican broke with tradition by confirming that private meetings would indeed take place.

"I am disgusted with Pope Francis, and utterly repulsed with how the Vatican has conducted itself in relation to this meeting," O'Gorman told CNN. "In terms of what needs to be addressed, it is of no value."