Pope Francis today reaffirmed Catholic opposition to gay marriage as he opened a three-week gathering of bishops from around the world but said the Church had to show love and understanding towards all.

Pope Francis presided at a solemn Mass in St Peter's Basilica to open the meeting, known as a synod, on the theme of the family in the modern world.

But the run-up to the synod, attended by some 300 bishops and other delegates, has been dominated by gay issues.

On the eve of the gathering, the Vatican dismissed a Polish priest from his Holy See job after he came out as gay and called for changes in Catholic teachings against homosexual activity.

Conservative Catholics held a conference in Rome just before the synod started on how homosexuals can live by Church's rules that they should be chaste while Catholic gay activists held another demanding full acceptance of active gays in the Church.

Pope Francis dedicated one third of his homily to the topic of love between man and woman and its role in procreation.

"This is God's dream for his beloved creation: to see it fulfilled in the loving union between a man and a woman, rejoicing in their shared journey, fruitful in their mutual gift of self," he said.

He also spoke of the "true meaning of the couple and of human sexuality in God's plan," a clear reference to heterosexual marriage. 

But Pope Francis also stressed that the Church must be more welcoming, charitable, compassionate and merciful to all people, particularly those whose lives have been wounded and who those find it difficult to adhere to all of the Church's regulations.

The leader of the 1.2 billion member Church said the person “who falls or errs must be understood and loved."

"The Church must search out these persons, welcome and accompany them, for a Church with closed doors betrays herself and her mission, and, instead of being a bridge, becomes roadblock," he said.

The Archbishop of Armagh and Primate of All Ireland Eamon Martin and the Archbishop of Dublin Diarmuid Martin, are representing Ireland's Catholic bishops at the Synod, which runs for three weeks.

Last week, Archbishop Diarmuid Martin told RTÉ News he expected there would be an opportunity, during the Synod, to discuss the issue of a Papal visit to Ireland with Pope Francis.

It followed speculation about such a visit after the Pontiff announced that the next World Meeting of Families will take place in Dublin in three years' time.

As bishops gather in Rome to review attitudes to modern family life women want their say.

The "Catholic Women Speak" network says the Vatican needs to "stop speaking about women in order to concentrate on speaking with women.”

Of the 360 or so people taking part in the three-week review, only 17 are women, called to speak strictly about their experience as wives and mothers.

"From silence to words, from subordination to responsibility, from invisibility to peace",  this is the battle cry of theological professor Cettina Militello, which has been taken up by women from all walks of life in the network.

The network's members include theologians, historians, journalists and researchers.

Most are mothers and all are deeply involved in the life of their parishes and frustrated that their skills are only valued at a local level.

But while some hope the Church's leaders will acknowledge that the number of Catholic nuns and lay religious in the world far outweighs that of priests, some 700,000 to 415,000, others are more realistic about their chances.

Speaking at a "Catholic Women Speak" meeting this week, former president Mary McAleese said it was an open secret that the synod was "the single most boring council on the planet".

"Pope Francis this month said that women are more important than men because the Church is feminine, can you imagine that?" she said, adding that the pontiff's actions on this front have so far fallen very short indeed.