The pace of modern life and the restless search for short-term material gain in a globalised economic system constitute a threat both to the planet and to human identity, Tony Blair has warned fellow Catholics.

In a speech to the prestigious Communion and Liberation conference at Rimini in Italy the former prime minister and Middle East Quartet envoy also told people of all faiths around the world that their own conflicts and divisions "allow aggressive secularism in part of the West to gain traction" when the faiths should be united in standing up for justice and solidarity.

"This is surely the role of faith in modern times. To do what it alone can do. To achieve what neither a person, nor a state, nor a community, on their own or even together, can achieve.

"To represent God's Truth, not limited by human frailty, or by the interests of the state or by the transient mores of a community, however well intentioned; but to let that truth bestow on us humility, love of neighbour, and the true knowledge that indeed passes all understanding." .

Blair spoke on a stopover during his family summer holiday in the Mediterranean where he was photographed and – not for the first time – criticised as a guest on Rising Sun, the five-deck yacht of American software billionaire Larry Ellison, anchored off the Sardinian coast.

The speech, delivered on Thursday, was partly personal, but also political in tone. In remarks which he admitted were "humbling" – as a new member of the Church addressing such a body – Blair credited his Catholic wife, Cherie, for his eventual formal conversion from Anglicanism shortly after leaving Downing Street in 2007.

"Ever since I began preparations to become a Catholic, I felt I was coming home; and this is now where my heart is, where I know I belong," he said.

Blair, who runs his own faith foundation, said his frequent visits to China had allowed him to see how both government and people of all faiths – including Catholics – were edging their way towards accommodating both modernisation and a sustainable, low carbon environment in ways that Westerners would recognise.