"Pope Francis has said that the Face of God is mercy. We come to Knock as pilgrims to glimpse that face, to be transformed ourselves so that we can take God's mercy to the world," he said in his homily.

"Being a pilgrim is responding to an invitation to receive Christ's message and be unburdened by Him who invites us: "Come to me all you who labour and are overburdened, and I will give you rest.'' We come to rest, to glimpse the revelation and to be renewed, but we also come to shoulder Jesus' yoke and learn from the one who is truly meek and humble of heart," he said.

Located in County Mayo, Knock Shrine is the location of an apparition of the Blessed Mother, St. Joseph, St. John the Evangelist, and a lamb and a cross on an altar that appeared on Aug. 21, 1879, at the gable wall of the Parish Church in Knock.

Fifteen people, between the ages of five and 74 years old, witnessed the apparition, and although it was raining, they said that the gable and the vision remained dry.

The witnesses gave testimonies to a Commission of Enquiry in October of that year, and the commission found the testimonies to be truthful.

"It is here that generations of pilgrims have experienced that God and Mary are indeed with us. As Pope John Paul said, pilgrims came here, especially those who are suffering, and they are healed, comforted, and confirmed in their faith," the cardinal said in his homily.

"The Irish have carried the faith to the ends of the earth, but this shrine of Knock is a place where Ireland's faith is nurtured. I am pleased to know that Knock is the most visited place in Ireland," he continued.

In his blog, the cardinal noted that in addition to the Boston pilgrims, "practically every bishop in Ireland" attended the Mass, as did "the papal nuncio, Archbishop Charles Brown, U.S. Ambassador to Ireland Kevin O'Malley, Taoiseach Enda Kenny," and a number of representatives from different Catholic organizations and associations.

"Lord Mayor of West Roxbury" Richie Gormley, one of the Boston pilgrims, noted that the Mass was "very beautiful," and said he counted "over 80 priests there."

Gormley helped organize the historic flight to Airport Knock, which he said was "most enjoyable flight I ever had in my life."

"It was very inspirational," he said, noting that he was honored to have been able to fly with Cardinal O'Malley.

"Cardinal O'Malley was a great host, and we were all there to support him," said Gormley.