The symposium is part of the International Eucharistic Congress celebrations taking place in Ireland and precedes the full program of events scheduled to begin in Dublin June 10.

Cardinal Ouellet told delegates -- including Irish Cardinal Sean Brady, as well as international bishops and theologians -- 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."

In an address described by Dublin Archbishop Diarmuid Martin as a "masterly synthesis" of the pastoral challenges faced by the church in terms of evangelization, Cardinal Ouellet explored the integration of the theology of communion with the theology of marriage, the development of the sacraments of initiation, the priesthood and the relationship between baptism and the ordained ministry and their significance in the life of the church.

The cardinal said one of the important tasks for theology in relation to pastoral practice was to integrate and reattach the manifestations of eucharistic piety such as adoration of the Blessed Sacrament, eucharistic processions and private Masses.

Adoration of the Blessed Sacrament must not be "belittled as a pious but now outdated custom," he said and added that the dialogue among theologians, pastors and the faithful "must be carried out in a climate of openness and respect for spiritual traditions."

Before his address the cardinal, who as archbishop of Quebec hosted the 49th International Eucharistic Congress in 2008, rang the congress bell "as a symbol that gathers us together." More than half a million people, including Pope Benedict XVI, have rung the bell.

The challenges to marriage were highlighted earlier in the day by Cardinal Oscar Rodriguez Maradiaga of Tegucigalpa, Honduras.

Cardinal Rodriguez defended the church's discipline on clerical celibacy to reporters and rejected the suggestion that celibacy was to blame for the shortage of priests in the church.

"It is not celibacy that is the problem. The problem is a life commitment. You see the same issue in marriage. Many people do not want to be married because they have a difficulty in committing for ever," he said.

Cardinal Rodriguez, president of Caritas Internationalis, the church's umbrella organization for charities, said the Eucharist was at the heart of the church's charitable action.

"Without the Eucharist, Caritas Internationalis could not be present as it is now in 164 countries of the world," he said.