Pope Francis has opened a synod – or meeting of Roman Catholic bishops from all over the world – that, this time, includes lay people and women. A number of thorny issues are on the agenda over the next few weeks – all behind closed doors.

With a solemn Mass in Saint Peter’s Square Wednesday, Pope Francis formally opened a four-week meeting that gathers 365 select members with voting rights, including lay people and not just bishops. It will also see women voting for the first time.

No binding decisions will be made, but controversial topics are up for discussion at the closed-door meeting, held in Vatican City’s Paul the Sixth Hall. They include the role of ordinary Catholics – including women – in decision-making processes; whether priests should be allowed to marry; and the church’s teachings on divorce and LGBTQ issues.

The theme of the meeting is “For a Synodal Church: Communion, Participation, Mission.”

Commentators say it is likely to expose deep divisions between liberals and conservatives in the Roman Catholic Church.

In his homily at Wednesday’s Mass, Pope Francis said church leaders at the gathering “do not need a purely natural vision, made up of human strategies, political calculations or ideological battles.”

The pope added: “We are not here to carry out a parliamentary meeting or a plan of reformation. The synod, he said, is not a parliament.”

Before the start of discussions, five conservative cardinals called on Pope Francis to reaffirm the church’s doctrine on same-sex couples and the ordination of women. In a letter, they presented five questions and expressed their concern that some in church leadership are no longer proposing sound doctrine but “teachings according to their own likings.”

In a written response, the pontiff steered away from providing the yes-no answers the cardinals requested and observers say he appeared to be open to the possibility of blessing same-sex couples.

The 86-year-old pontiff said that “we cannot be judges who only deny, reject and exclude.” He wrote, “Pastoral prudence must adequately discern whether there are forms of blessing, requested by one or more persons, that do not convey a mistaken concept of marriage.”

At Wednesday’s Mass, Pope Francis said the synod aims to reaffirm “a church that looks mercifully at humanity,” and is “united and fraternal, that listens and dialogues; a church that blesses and encourages.”

Ahead of the meeting, Vatican officials said no media would be allowed and attendees were instructed to not speak to reporters about the discussions.