The fresh-faced bishop looked out at his congregation from the pulpit of the new chapel in the well-heeled Boston suburb of Belmont and began his Sunday morning sermon.

"Where much is given, much is required," he told those in the pews in front of him, emphasising the need to apply the scriptures in their homes, with their neighbours and at their work.

The year was 1985 and the bishop was a 38-year-old Mitt Romney. He and his wife Ann were raising a brood of five boys aged under 16 and he had just founded Bain Capital, a new player in the emerging world of private equity.

In the Mormon Church, whose clergy are lay and unpaid, Mr Romney was serving his third year as the bishop of his ward, the equivalent of a parish priest. In 1986, he was promoted to stake president for all Boston area congregations (comparable to running a diocese), a position he held until 1994 when he first ran for political office.

Even after standing down from leadership roles in the church to challenge for Edward Kennedy's Massachusetts Senate seat, he continued to teach the Sunday school classes attended by Mormons of all ages.

Indeed, Mr Romney has a life-time of service that would be campaign-trail gold dust for a candidate for America's highest office. But US voters will not hear about it from the mouth of the man who will soon be formally confirmed as the Republican presidential nominee.

He frequently highlights his chosen credentials for the top job - private sector expertise as a corporate high-flyer, "saviour" of the floundering 2002 Salt Lake City Winter Olympics, former Massachusetts governor and family man.

Last weekend, he unveiled his vice-presidential running mate, Paul Ryan, a hawkish fiscal conservative who shores up Mr Romney's standing with the party's Right wing where suspicions are strong of his establishment background and reputation for "flip-flopping" on social issues.

It was his first major political move since returning from an overseas trip that also reinforced another reputation, this time for gaffes, after he offended his hosts in Britain by questioning London's readiness to stage the Olympics.

Mr Romney and Barack Obama are neck-and-neck in the polls, with all the indications suggesting the battle will be decided in a handful of swing states on November 6. Yet even though his biography is well known, for many Americans the real Mitt Romney remains something of an enigma - less than three months before the election that could make him president.

And even as the war of words in the race for the White House plumbed new depths in recent days, it is clear that Mr Romney will not discuss the faith that has shaped his life and character.

The data-driven former chief executive has decided the advantages of airing this would be outweighed by the down side: drawing attention to the details of a faith that many evangelical Christians call a cult, and some other Americans regard simply as "weird".

Members of the Church of Jesus Christ of Latter-Day Saints abandoned polygamy in the 1890s, although some factions still practise it. They all believe that the faith's founder, Joseph Smith, had visitations by Jesus and God in the woods of New York state in the 1820s and buried golden plates (the Book of Mormon) that details how Jesus Christ visited the Americas after his resurrection and will begin his Second Coming in Missouri. Such assertions disquiet many Americans, as does the practice of baptising anyone's dead ancestors into the Mormon faith.

Mormons, who eschew alcohol, tobacco, coffee and tea, are pro-life and are also taught that homosexuality is a sin. They believe that the US Constitution is a document inspired by God that makes America the new "Promised Land".

Mormon customs are often mocked, not least their undergarments. Ridiculed by some as "magic underwear", they consist of white undershirt and white boxer-style shorts with small sacred symbols to remind the faithful of the covenants they have made.

So Mr Romney's calculations may well be correct. Opinion polls suggest religion will not be a big influence on how Americans vote and Mr Obama's campaign has no intention of bringing faith into the election battle, not least as he had to fend off links to his black liberation pastor in the 2008 campaign.

But at the Belmont chapel with Mormons who have worshipped with Mr Romney for decades, The Sunday Telegraph was given a rare insight into his ecclesiastic career and how that shaped him.

The red-brick meeting house, whose opening in 1984 had been delayed by an arson attack, sits in gardens beneath the hill-top Boston temple, a structure of Sardinian granite, its spire topped with a gleaming golden angel.

Only Mormons with authorisation issued by their bishop can pass the front desk of the $30?million (pounds 19 million) temple, changing into all-white clothes for special religious ceremonies. The building was funded by worshippers who are expected to tithe 10 per cent of their income to the church and the Romneys, whose fortune is estimated at $250 million thanks to the success of Bain, were the largest contributors to what some locals call "Mitt's temple".

But the chapel where regular services and scripture lessons are held is open to all and it was there that two former church leaders last week shared their sharply differing views of a man with whom they have worked and prayed.

"Even as he ran his business and raised his family, Mitt always found time to meet the spiritual and temporal needs of his congregation," said Grant Bennett, a former Boston stake president who has known Mr Romney since 1978. "He was extremely diligent about his duties and organised his schedule to make room for church, family and work."

He related several stories of Mr Romney's pastoral care as he devoted hours each week to church duties that ranged from taking teenagers on skiing trips to meeting members to discuss problems in their lives, one-on-one.

"In his sermons, one of the themes that I often heard Mitt discuss was 'Where much is given, much is required'," said Mr Bennett, who worked with Mr Romney at the Bain consulting business before the establishment of Bain Capital and now runs an electric components company. "That's why he's running for president. There is a simple and genuine element of Mitt wanting to give back.

"Central to his Sunday school teaching was how to apply the scriptures to live lives of honesty, forgiveness, tolerance and kindness."

Mr Romney's critics say it is those tenets - and his undisputed record of good works in his private life - that are in sharp contrast to his business career at Bain. The company has become a lightning rod on the campaign trail as symbolising "vulture capitalism" for the companies that it closed down and workers it laid off.

Mr Bennett instead sees evidence of Mormon traditions of self-reliance in the candidate's economic message. "He believes that many of society's ills are best addressed by families working together and individual morality," he said. "Government is not always the answer." He also cites the analytical skills that Mr Romney picked up taking dual degrees at Harvard's business and law schools.

"I wish Mitt would talk more openly about his personal life and church service," he said. "But it makes sense to me that he has analysed the situation and decided that he wants to focus on the economy and that he does not want to give people the chance to raise old misconceptions about our faith."

But Tony Kimball, another long-time colleague, said he was "shocked" by Mr Romney's "end justifies the means" approach to trying to win the White House.

"There is no way that I can square what Mitt is doing and saying on the campaign trail with the Mitt I have known for 40 years and I don't know how he can square it either," said Mr Kimball, a retired university politics professor who served as another Boston area bishop and then spent seven years as Mr Romney's executive secretary when he was stake president.

"I am dismayed by the things he feels the need to do as a political candidate. This is foreign to the way he spoke and presided in the church. It's not the same person.

"The hard-edged individualism, the turning his back on the poor, the arguing that the rich deserve more tax breaks, that is all counter to what Mormonism teaches about compassion and collective care.

"Mitt seems to create a caricature of Obama and the Democrats and then attacks that creation. I think he lacks the antennae that a good politician needs and I have serious misgivings about how he would manage the White House."

Mr Romney did have Mormon detractors back in his days as bishop and stake president. Among the most vocal was Judith Dushku, the editor of a feminist Mormon magazine who clashed repeatedly with Mr Romney. "His attitude is always, 'I know what's best. I'm the interpreter of Mormonism for all Mormons and you have no right to comment on it and if you do comment on it, you're wrong,'" she told CNN recently.

Most notably, a mother of four published a letter in the magazine in which she said that her bishop - whom she later identified as Mr Romney - put pressure on her not to have an abortion despite developing a blood clot that put her health at risk when she became pregnant for the fifth time in her mid-40s. Mr Romney has since said that he does not recall issuing such specific instructions.

Sandy Catalano had a very different experience, however. A former Roman Catholic, she converted to Mormonism in the early 1980s, but her husband Ron viewed her new faith as a cult and the strain almost destroyed their marriage. Then she fell ill, and as Mr Catalano struggled to care for their two children, Mr Romney took time off work and arranged for church members to help the couple.

"Ronnie started to realise that the church was full of kind people, although he was still sceptical about some of the tenets," she said. "Then he lost his photography business and Mitt came up with maintenance jobs for him do around the church. He went out of his way to help Ronnie find work and maintain his integrity."

Her husband converted to Mormonism 11 years after his wife. "I have seen Mitt help hundreds of people in our sort of situation," she said. "He genuinely cares and is very compassionate. I wish more people knew that about him."

On the campaign trail, it is left to Mr Romney's wife Ann - as natural as he is stiff - to provide the personal touch that he seems unwilling or unable to deliver. Last week, she recalled how they both welled up with tears when she was diagnosed with multiple sclerosis in 1998, the year before they moved to Utah so that Mr Romney could step in and head the Winter Olympic organising committee.

She also disclosed that her MS, long in remission, had briefly flared up again under the pressures of the Republican primary battle this spring. Initially, Mrs Romney did not even tell her husband, concerned that it would undermine his campaigning.

The couple's five clean-cut sons - two in finance, two in real estate and one a doctor - their wives and 18 grandchildren often join the Romneys at campaign events that invariably convey an image of family wholesomeness.

It was as a 21 year-old that Mr Romney was plunged into his first experience of a leadership role by tragedy during his time as a young missionary in France in 1968. He was driving Duane Anderson, the mission president, and his wife to a meeting when another car on the wrong side of the road smashed head on into their vehicle.

Mr Anderson's wife was killed and Mr Romney was left in hospital with serious injuries. But after he recovered, he was drafted in as acting president of the mission office.

His family history is inextricably linked to such missions. His great-great-grandfather Miles Romney, a carpenter from Dalton-in-Furness, converted to the religion in 1837 after hearing the first overseas missionary speak near Preston. Miles and his wife subsequently emigrated to the US in 1841.

Mr Romney's father George was born in Mexico in an enclave set up by Mormon polygamists fleeing sheriffs in America after the practice was outlawed. George's parents moved back to the US when he was five and he later became head of American Motors, governor of Michigan and ran unsuccessfully for president in 1968.

It is all part of a compelling story that would feature prominently for many presidential candidates - but not, it seems, for Mitt Romney, even as he prepares to take centre stage at his party's nominating convention in Tampa next week.