Oullet, head of the Congregation for Bishops who is acting in Dublin as papal legate, told delegates that the Church must promote the family in this time of "unprecedented anthropological crisis ... characterized by the loss of a sense of marriage and the family."
On a day that the Congress program focussed specifically on marriage and the family, Hickey told a packed conference hall that "only a few years ago one could safely assume that our understanding of marriage was generally accepted," but this is no longer the case.
"Increasingly marriage is being promoted as only one of the many options in human sexual relationships," he said. "Recent years have witnessed a sharp rise in cohabitation before marriage. These so-called partnerships are even taking the place of marriage."
He said that "adding to this is the pressure to change the very definition of marriage from a union of a man and a woman to a union of two persons of the same sex."
"The ideal of Christian marriage is under great threat," he warned.
He said that "the availability of easy divorce undermines the strength of commitment that true marriage requires and encourages the view that marriage is no longer a permanent contract."
The archbishop said that "this worsening situation is all around us, yet it is rarely the subject of political debate.
"It calls for urgent action at all levels of society. The family is under threat because the institution of marriage is being undermined," he said.
In his address, Carl Anderson, supreme knight of the Knights of Columbus, criticized a tendency to see marriage merely as a contract.
"Without sanctification, the family's gift of self becomes reduced to a mere consensual agreement or, as one American law school textbook on family law described marriage, as being better understood today as 'a joint venture for profit between the spouses.'"
He warned that "too often the cultural commentary about marriage — especially found in defense of divorce — suggests marriage and family is risky because one's commitment and contribution may not 'pay off' — that there may not be an adequate return on one's investment in the marriage."
Encouraging families to draw strength from prayer, Cardinal Andre Vingt-Trois of Paris said the Church "must not rule out anything of all that can be done publicly to defend the value of the family."
However, he said that "the first mission of Christian families is to live concretely by these values, by reconciliation, mutual acceptance and joy in giving one's life for one's loved ones."
"The strength of our testimonies lies in the examples we give. The Church will be heard and respected inasmuch as she helps Christians remain irreversibly faithful, confident enough to welcome new lives, tirelessly kind to the oldest and to the most vulnerable, and respectfully open to the ones who are alone," he said.