Both living Popes, Francis and Benedict XVI, have come together to send an unprecedented message against gay marriage.

A new ‘encyclical’ issued by the Vatican today, contains their joint musings on the nature of faith and love. It says faith should serve the ‘common good’ but makes clear this doesn’t include gay and lesbian marriage.

The document, only signed by Francis but promoted by Benedict XVI who came out of retirement today to push it, says faith enlightens humanity ‘first and foremost’ by ‘the stable union of man and woman in marriage’.

While same-sex marriage equality is not mentioned in name, the passage that follows makes it clear both Francis and Benedict intend to condemn it.

They say heterosexual unions are ‘born of their love, as a sign and presence of God’s own love’.

And they insist straight marriage is ‘the acknowledgment and acceptance of the goodness of sexual differentiation, whereby spouses can become one flesh’ – in other words sex should be between men and women in marriage.

They then go on to put the procreation of children at the center of their faith.

They say: ‘Faith also helps us to grasp in all its depth and richness the begetting of children, as a sign of the love of the Creator who entrusts us with the mystery of a new person.’

And they attempt to put religion above human rights by saying the idea of equality without faith ‘cannot endure’.

Francis’ views are not surprising. Although it is the first time he has made such a clear statement since becoming Bishop of Rome, he caused controversy when still a cardinal in Buenos Aires by attacking Argentina’s moves towards gay marriage.

He said it would ‘seriously harm the family’ adding: ‘At stake is the identity and survival of the family: father, mother and children.

‘At stake are the lives of many children who will be discriminated against in advance, and deprived of their human development given by a father and a mother and willed by God. At stake is the total rejection of God’s law engraved in our hearts.’

Francis said Benedict XVI wrote most of the ‘encyclical’ before resigning and he merely added ‘further contributions’.

The documents are papal circular letters addressed to Roman Catholic clergy to summarize a pontiff’s opinions.

They are treated seriously. It was in encyclicals that Paul VI banned the use of contraception and John Paul II called on the faithful to fight laws legalizing abortion.

To promote this one, Francis and Benedict embraced each other this morning (5 July) at the inauguration of a new monument inside the Vatican gardens.

It is the first time they have been seen together since 2 May when Francis welcomed Benedict back to the Vatican after his initial time away when he entered retirement.