Archbishop of Armagh and Primate of All Ireland Eamon Martin said that the family is decisive for the future of the world.
At the World Meeting of Families in Dublin he said: "We must work with all people of goodwill to encourage the state to support the family, and especially the uniqueness of the faithful and exclusive union between a married man and a woman as a beloved space for carrying and raising children.
"By doing this, the state not only cares for its citizens, but also strengthens and cherishes the foundations of society itself."
Archbishop Martin had replaced Archbishop of Washington Cardinal Donald Weurl as keynote speaker.
Cardinal Weurl withdrew from the publication of a critical report in the US on the treatment of cases of clerical sexual abuse.
The archbishop also touched upon recent remarks from Pope Francis when he said that the family "deserves special attention from those responsible for the common good".
The pope had said that the family was the "basic unit of society, which establishes strong links between trade unions that underlie the coexistence of people and, with the revival and upbringing of children, ensure the renewal and future of the society".
Archbishop Martin said that the Catholic Church did not suggest that it wanted the state to overreact or replace the important autonomy of the family.
He said: "We believe that if the institution of the family is damaged, the whole society suffers.
"As the vital circle and community of love and support in society, the family is much more than an economic or social unit, it is a privileged space for care, education, health promotion, mediation, security, community cohesion and security."
Earlier, the head of a lobby group for the homeless said that the & # 39; huge deficit & # 39; to homes in Ireland has allowed families in Dublin, on the street, in tents and hostels, to sleep.
Fr Sean Donohoe, co-director of Capuchin Day Center in Dublin, spoke on the second day of the World WMOF.
Pope Francis will visit the center on Saturday as part of his visit to Ireland.
Founded by Capuchin Brother Kevin Crowley, the center offers 1,000 hot meals a day, clothes and showers to the homeless in Dublin.
Fr Sean said that although the center can not solve the homeless crisis, it could alleviate the problem.
He spoke during a panel discussion about homelessness entitled No Room At The Inn.
"There is a huge shortage of housing in Ireland," he said.
"We have homeless people who are clear to us, who sleep on our streets, in tents, in hostels and emergency centers and hotels.
"We still have other people living at home who, like young adults, have lived at home for a long time and can not buy a house.
"There are people who sleep on couches, they too are homeless even though they are not included in government statistics because they are supposed to be accommodated.
"Although there is no doubt that there is a crisis, I am also convinced that there is a lively Christian reaction in our culture."
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He spoke about the work of the Capuchin Center and its goal to provide food and shelter for the homeless.
"In the center we have a doctor, a nurse, a dentist, a social worker and a hairdresser," he said, adding that hundreds of people daily use their services.
"We can not solve the homeless problem in our country, we can alleviate the situation for those who have nothing."
Also during the event was Conor Hickey, chief executive of Crosscare, a charity for social support of the Catholic Archdiocese of Dublin, who said that homeless families did not exist three years ago.
He said: "Traditionally, homeless people are associated with a person who may have a number of problems.
"The current homeless crisis is determined by families and individuals who do not have houses.
"Families who, through economic problems of their own control, struggled to find somewhere to live."
Thousands of pilgrims are expected to attend events for the WMOF, with 37,000 people and families attending the pastoral congress in the RDS during the week, attending workshops, panel discussions and exhibitions.
Nearly 300 speakers will participate, where topics cover the impact of technology on families, with respect for LGBT members of parishes and the protection of children and vulnerable adults.
The WMOF event was officially opened last night by Archbishop of Dublin Diarmuid Martin.
In a video message that Pope Francis had issued last night, he said he was excited at the idea of returning to Ireland, where he spent three weeks with the Jesuit community at Milltown in Dublin, where he learned English in 1980.
His message was released after the Vatican had confirmed that he would meet survivors of sexual sexual abuse here.
The World Meeting of Families closes on Sunday with open air at the Phoenix Park in Dublin, an event for which 500,000 tickets have been issued.
Skoda, who is the official & # 39; popemobile & # 39; supplies to the Pope, has unveiled a special stained glass vehicle that will be on the RDS at the Pastoral Congress.
More than 1700 individual pieces of glass were cut by hand and embedded in 25 meters of lead, in traditional church style, to complete the project.
This is purely a display model and will not be controlled with the stained-glass window.
After the visit, the vehicles are donated to a charity to be nominated by Archbishop Diarmuid Martin, in accordance with the wishes of Pope Francis.
Additional reporting PA