In his homily, Archbishop Aupetit stressed the purpose of Notre Dame as a place of Christian worship, and not an ornament of the secular state.
Pope Francis also visited the Roma, or Gypsy, community, asking forgiveness for times when the Church excluded them.
The decision to allow organized pilgrimages, banned by the local bishops' in 1991, recognizes the need to provide spiritual accompaniment and care to the tens of thousands of Catholics who travel to Medjugorje each year.
The attack on the Catholic Church during Mass killed six people, including a priest.
Vanier founded L'Arche communities. There is one L'Arche community on Long Island in Riverhead.
At the Vatican, after his Easter blessing, Pope Francis expressed his sadness by over the bombings in Sri Lanka.
Bishop Barres says he joins "in sorrow and prayer" with our Catholic brothers and sisters in Paris.
Bishop: "Horrific and cowardly" attack has made this country "a land of heartbreak."
Click here for more photos of our Diocese of Rockville Centre pilgrims at World Youth Day.
The attack "on a sacred day and at a sacred moment of worship" was "the action of evil people with utter disregard for the sacredness of human life and of human dignity."