Pope Francis will on Friday issue new guidelines on the Church's approach to love, sex and marriage in what is being billed as one of the defining moments of his tenure.

Is he gay-friendly and relaxed about divorce and cohabitation? Or is the pontiff a conservative who understands the need to sidestep issues that put the Church at odds with how many believers live in the 21st Century?

The verdict on the 79-year-old Argentine's legacy will in large part be framed by the contents of the document on the family that will be published on the stroke of noon.

Officially referred to as an "apostolic exhortation", the 200-page text is effectively a letter to the world's 1.2 billion Roman Catholics that lays down revised foundations for Church teaching and pastoral practice on a host of issues related to family life.

The hopes of Catholic radicals for significant changes to official doctrine were quashed during the 2014 and 2015 synods of bishops, the conclusions of which will inform without dictating the content of Francis's missive.

But the document will also inevitably reflect the current pontiff's instinctive tendency to try to make the Church seem a more merciful, less judgemental body in relation to those faithful who find themselves in "irregular" situations.

Influential German cardinal Walter Kasper has predicted that the exhortation will mark a "turning of the page" for the Church.


Amoris Laetitia

"Who am I to judge?" Francis said early in his papacy when asked about how the Church should deal with gay believers who, some Catholic theologians now think, have no choice about their sexuality.

That comment and the radical language contained in an early draft of conclusions from the first synod on the family raised progressive hopes of a great leap forward in Catholic teaching on vexed questions such as whether divorced and civilly remarried believers should be allowed to take communion.

But the strength of conservative opposition -- led by bishops from the developing world -- to a substantial relaxation of the Church's model of what the ideal family looks like has made it unlikely that will happen.

Francis, say those who know him best, is nothing if not a pragmatist and the last thing he wants on his watch is a schism over what he once called "below the belt issues" which he regards as having assumed far too much importance in the life of the Church.

The exhortation, entitled "Amoris Laetitia", is to be presented at the Vatican by Cardinal Christoph Schoenborn, the archbishop of Vienna who is seen as a moderniser and is himself the son of divorced parents.

It will also be unveiled in dioceses around the world with local bishops having already been sent guidelines on how to explain the changes to their congregations.