A leading contender to become the next Pope has launched a fierce attack on the forces of secularism, arguing that they were fostering intolerance in Europe and forcing Christianity underground.
Cardinal Joseph Ratzinger, 77, one of the Vatican's most powerful figures, said that liberal consensus had now evolved into a "worrying and aggressive" ideology.
As a result, "Catholic and Christian religion" had been pushed out of the public debate and was being "driven into the margins".
The warning, in a long interview in La Repubblica, comes as the Bavarian-born cardinal, who is the Pope's doctrinal chief, is being viewed as an important late entry for the papacy.
Coming shortly after European Parliament MPs refused to approve the Italian politician Rocco Buttiglione as European justice commissioner because of his strong Catholic views on gays and women, his statements might be seen by some as something of a manifesto. The cardinal was speaking against a backdrop of rapidly declining priestly vocations in Europe, which was worrying Church leaders.
Describing the development of a "secular ideological aggression" across the continent as "cause for concern", the cardinal said: "In Sweden, a Protestant minister who preached about homosexuality on the basis of an excerpt from the scriptures was put in jail for a month.
"Secularism is no longer that element of neutrality, which opens up space for freedom for all. It is beginning to change into an ideology which, through politics, is being imposed.
"It concedes no public space to the Catholic and Christian vision, which, as a result, runs the risk of turning into a purely private matter, so that deep down it is no longer the same.
"In this sense, a struggle exists and so we must defend religious freedom against an ideology which is held up as if it were the only voice of rationality, when instead it is only an expression of a 'certain' rationialism."
He said that in contemporary society, God had been pushed "very much into the margins".
"In politics, it seems to be almost indecent to speak about God, almost as it were an attack on the freedom of someone who doesn't believe. A secularism which is just, is a freedom of religion. The state does not impose a religion, but rather provides free space to those religions with a responsibility to civil society.
"Negative birthrates and immigration are changing Europe's ethnic make-up. Above all we've gone from being a Christian culture to one of aggressive secularism, which at times is intolerant."
He said even though "churches were emptying" and people were "no longer able to believe," Christian faith was "not dead".
The cardinal remained convinced of hope's inner strength, even if the future of the Catholic church lay more in "other continents" than Europe.
Cardinal Ratzinger, once viewed as the likely papal "king-maker", is believed to stand a good chance of becoming the next Pope because of his advanced years.
Vatican watchers maintain that long-serving Popes tend to be succeeded by short-lived "interim" papacies.