At a special Mass in Knock Basilica, Cardinal Ouelett explained he had been asked by Pope Benedict to come on his behalf to Ireland's Marian shrine.
The cardinal said the Pope prayed daily "that the people of Ireland may know the Lord's peace, consolation and comfort".
He continued: "Let us be confident there is light beyond this present darkness and that our faith is stronger than the evil of this world and our own failures."
Further on in his homily, Cardinal Ouelett said family life was often tested and strained by tensions, separations and misunderstandings.
He added: "We need hope and renewal at all levels."