His life as a pastor/lawyer in the backstreets of Melbourne’s St Kilda, and as CEO then chief advocate for the giant World Vision Australia aid agency charity is familiar territory – retold winsomely in his new memoir, A lot with a Little.

But just how has he married his faith and his advocacy has made him a figure of controversy among some Christians.

“In a gentle way, this book tries to address the Australian church through the story of my parents” – Tim Costello

At the book launch at Sydney’s Gleebooks last night, an audience member asked Costello how he regarded the mainstream church – which, for them, was on the wrong side of several social questions of the moment. Costello, probably rightly, took it as a question of how can you be both a social activist and a Christian.

The answer is found way back in the courtship of Russell and Anne Costello, Tim’s parents. “In a gentle way, this book tries to address the Australian church through the story of my parents,” he told the book launch crowd.

Russell was a member of the Melbourne University Evangelical Union (EU), fresh from having used his returned serviceman’s Commonwealth Training Scheme money studying at Melbourne Bible Institute – the very heart of evangelical Melbourne. He came to hold the record for going to the most beach missions – as Tim says in the book, “such was his zeal.”

Anne belonged to the rival Student Christian Movement (SCM) – which has been eclipsed by Australian Fellowship of Evangelical Students, which often is the largest Christian student club on Australian campuses. SCM is more outward looking, more liberal in its theology and happy to meet and discuss or hear talks on social and political issues of the day.

Russell and Anne met and married from opposite sides of this religious divide. “SCM and EU were the Sunni and Shia of Christianity,” Costello told his audience.

Russell, who passed away in 2016 but is larger than life in the book, met Anne when SCM and EU were in competition to teach Religious Studies at University High – close by the uni. Tim recounts it this way in the book: “One day Russell attended a required joint meeting of the SCM and EU to co-ordinate the curriculum they were all supposed to be teaching. An outgoing bright girl asked, ‘What religious books from the curriculum syllabus will be using to teach religious studies?’

“The supervisor muttered, ‘Good question, I’ll get back to you about that.’

“After the meeting Russell went up to her. ‘I know a great book that I am going to teach from.’

“The bright young girl took out a notebook to write down its name and Russell, grinning, said ‘It’s called the Bible.’

“She looked aghast.”

The marriage worked. Tim Costello has emerged as a “both/and” Christian. “My formation was between those two bookends,” he said at the book launch. “Dad the evangelical, and Mum more of the “thy kingdom come, thy will be done on earth as in heaven.

“I am addressing the church through the Christian experience of my parents.,” he said again.

“Faith is a synonym for risk,” he told a questioner who asked him to explain faith. “If there is no risk, there is no need for faith.”

He has drawn on faith during his journey, giving up the offer of a partnership in a successful Melbourne law firm to go penniless to study theology in Switzerland – away from the powerful influence of his evangelical father. He describes meeting Italian Baptists who voted Communist and, perhaps worse, British and German Baptists who smoked and drank.

“The good news is for those who are poor, spiritually poor and physically poor” – Tim Costello

He summarised his creed for the Gleebooks crowd: “The good news is for those who are poor, spiritually poor and physically poor.” A both/and Christianity captured in a paragraph.

For his Sydney audience, Tim Costello described the St Kilda he started ministry in as, “a giant sinkhole for abandoned kids and street people.” He had taken the “wrong” church, a red brick building in a depressing side street that the powers-that-be had decided to close. But as he observed, “I would have shrivelled up inside as a pastor in Melbourne’s Bible belt”. In St Kilda he was able to grow.

But there were lessons to learn from the people, such as Eva, a member of the Stolen Generations.

“I remember struggling with how Eva juggled her genuine faith with her psychiatric disorder and lifestyle of surviving from pension cheque to pension cheque. Was this living life in all its fullness? Yet I was deeply moved by the fact that she would give away her last dollars to a hungry neighbour or anyone in need, not knowing if she could eat until the next pension cheque. How was that responsible? I wouldn’t do that. But she would just say, ‘But God will provide.’ She was actually living by faith; I only preached it as an ideal. I didn’t trust God in the way she did. Few Christians I admired did.”

Costello’s statements about faith can be quite guarded, from the perspective of this evangelical at least. But to the Gleebooks audience, he declared his faith in the resurrection, also describing himself as “an orthodox Christian.”

He is no naïve progressive, idolising mankind. “God wants us to flourish. God wants us to overcome the wiring that makes us have a predilection for malevolence and greed.”

But the newly-appointed fellow at Centre for Public Christianity is also a critic of the right-hand part of the church.

“I am a bit saddened at the reductionism of the conservative parts of the church,” he said, by which he means a narrow focus on “moral” issues.

He’s critical, too, of both the left and right in a society that is polarising “Social media has got us. ‘You disagree with me’ equals ‘I hate you, and you hate me.’”

He wants a society where we can still talk. Like Russell from EU and Anne from SCM.

A Lot With a Little: The Long Awaited Memoir of Australia’s Favourite Activist and Man of the People by Tim Costello (Hardie Grant Books) is $44.99 from Koorong and other leading bookstores.