Pope Francis risked further angering conservatives in the Catholic Church today by urging opponents of abortion to show equal passion for the oppressed and stating that 'excessive importance' should not be given to certain Church rules while others are disregarded.

The pope made his controversial appeal in a new major document known as an Apostolic Exhortation, called Gaudete et Exsultate (Rejoice and be Glad), a 100-page booklet on how people can be holy in a modern world filled with secular distractions and materialism.

In it, he urged people to try to be 'the saint next door' by doing good and living out the gospel as much as they could and keeping charity and mercy, rather than rigid rules, at the centre of their lives.

He said that sainthood was not only for bishops, priests and nuns or those 'swooning in mystic rapture' but also for people living ordinary lives, with small gestures, patience and love.

And he appeared to take a swipe at some conservatives who swear by the rigid letter of doctrine and 'the thicket of precepts and prescriptions' while not always showing mercy or compassion towards individuals.

'Not infrequently, contrary to the promptings of the [Holy] Spirit, the life of the Church can become a museum piece or the possession of a select few. This can occur when some groups of Christians give excessive importance to certain rules, customs or ways of acting,' said Pope Francis.

In the document, he said Catholics should not 'relativise' different aspects of Church social teachings by giving priority or their undivided attention to a single ethical or moral issue while caring less about social problems such as immigration.

"Our defence of the innocent unborn, for example, needs to be clear, firm and passionate, for at stake is the dignity of a human life, which is always sacred and demands love for each person, regardless of his or her stage of development,' he wrote.

'Equally sacred, however, are the lives of the poor, those already born, the destitute, the abandoned and the underprivileged, the vulnerable infirm and the elderly exposed to covert euthanasia, the victims of human trafficking, new forms of slavery, and every form of rejection.'

He urged Catholics not to 'uphold an ideal of holiness that would ignore injustice in a world where some revel, spend with abandon and live only for the latest consumer goods, even as others look on from afar, living their entire lives in abject poverty'.

The Reuters Vatican correspondent Philip Pullella speculated that Francis appeared to be referring to Catholic groups in some rich counties, such as the US, who passionately oppose abortion while at the same time oppose legislation to help immigrants.

The pope said that Catholics who considered social justice a 'secondary issue compared to the "grave" bioethical questions' were like 'a politician looking for votes'.

He added that for a Christian, the 'only proper attitude is to stand in the shoes of those brothers and sisters of ours who risk their lives to offer a future to their children'.

Additional reporting by Reuters.