Pope Francis told a key Roman Catholic meeting on family issues on Monday that the Church should not be a hidebound "museum of memories" but have the courage to change if that was what God wanted.

The three-week meeting of bishops from the around the world will discuss ways to defend the traditional family and making life-long marriage more appealing to young people while seeking common ground with disaffected Catholics such as homosexuals and those divorced.

The Synod, attended by some 300 bishops, delegates, observers and 18 married couples, has been preceded by intense jockeying between conservatives and liberals on a number of sensitive issues.

In his address to open the first working session, Francis said the bishops should not just talk but try to hear what God wanted for the Church of 1.2 billion members and to listen to differing opinions among themselves.

He urged the bishops to humbly empty themselves of conventions and prejudices to listen to their brother bishops. They should not "point fingers at the others to judge them" or feel superior to those with different ideas.

In a nod to conservatives, he called for courage that "does not let itself be intimidated by the seductions of the world" and passing fads.

But, in a passage that appeared to be directed at unbending traditionalists, he said the bishops should also beware of the "hardening of some hearts, which despite good intentions, keep people away from God".

He said Christian faith was "not a museum to look at and save" but should be a source of inspiration. Francis called on the bishops to have "courage to bring life and not make our Christian life a museum of memories".

The bishops, who are meeting behind closed doors, will submit reports to the pope. He may use these to write his own document, known an Apostolic Exhortation, on family issues.

Follow-up to stormy meeting last year

The meeting is the final follow-up to a similar meeting held a year ago. That gathering was marked by stormy differences between conservatives and liberals on how much the Church should approach the question of homosexual Catholics.

The immediate run-up 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 rules that they should be chaste, while Catholic gay activists held another demanding full acceptance of active gays in the Church.

In its explanation of the firing of the Polish monsignor on Saturday, the Vatican said his very public coming out was intended to put undue media pressure on the synod.

Francis appeared to make a reference to outside pressure when he said the synod should be "a protected space were the Church feels the action of the Holy Spirit".

Another key topic will be how to involve Catholics who have divorced and remarried in civil ceremonies.

They are considered by the Church to be still married to their first spouse and living in a state of sin. Some bishops want a change to the rules that bar them from receiving sacraments such as communion.

Last month, Francis made it simpler and swifter for Catholics to secure a marriage annulment, the most radical such reform for 250 years. He told bishops to be more welcoming to divorced couples.