Making by far his most spiritual speech of his presidential campaign, Republican Mitt Romney on Saturday offered a fierce defense of Judeo-Christian values and an America that he said “has trusted in God, not man.”

Romney sought to root his candidacy in faith with a commencement address at Liberty University in which he spoke of a shared “Christian conscience” to bridge his Mormon faith with that of evangelical Christians. But the all-but-certain nominee largely sidestepped divisive social issues in his speech to more than 6,000 graduates and some 30,000 of their friends and family members here at one of the nation’s most influential bastions of political and Christian conservatism.

Although Romney spoke of common spiritual values, he did not discuss his personal faith. The candidate who is poised to make history as the first Mormon to win a major party’s presidential nomination made no reference to his Mormonism.

“Central to America’s rise to global leadership is our Judeo-Christian tradition, with its vision of the goodness and possibilities of every life,” Romney said. “From the beginning, this nation has trusted in God, not man. . . . There is no greater force for good in the nation than Christian conscience in action.”

Romney journeyed to this bucolic campus in the foothills of Virginia’s Blue Ridge Mountains at a pivotal moment in his campaign. By simply visiting the university founded in 1971 by the late televangelist Jerry Falwell — a campus that rose to national prominence during the Moral Majority movement of the 1980s — Romney made his most overt play yet for support from within the evangelical movement.

But although Romney tried with Saturday’s speech to unite Christian conservatives who had resisted his candidacy through a polarizing Republican primary, he also sought to appeal to the country’s moderate middle — the independent voters who could prove decisive in key battleground states this fall.

The candidate largely ignored the cultural issues that are dividing the nation’s electorate, and he neither mentioned President Obama by name nor delivered the attack on Obama’s economic stewardship that has become the cornerstone of Romney’s campaign.

Romney made a single reference to gay marriage, a hot-button issue thrust into the news this week with Obama’s announcement that he supports letting same-sex couples wed.

“Culture — what you believe, what you value, how you live — matters,” Romney said. “As fundamental as these principles are, they may become topics of democratic debate from time to time. So it is today with the enduring institution of marriage. Marriage is a relationship between one man and one woman.”

At that, the audience rose to its feet and gave Romney the loudest ovation of his speech.

Most of the address, however, was a tour through the religious values that Romney said defines the American experience.

“What we have, what we wish we had — ambitions fulfilled, ambitions disappointed; investments won, investments lost; elections won, elections lost — these things may occupy our attention, but they do not define us,” Romney said. “And each of them is subject to the vagaries and serendipities of life. Our relationship with our Maker, however, depends on none of that. It is entirely in our control, for He is always at the door and knocks for us.”

Romney laced his speech with references to a diverse assortment of Christian leaders, including author C.S. Lewis and civil rights icon Martin Luther King Jr. “Christianity is not the faith of the complacent, the comfortable or of the timid,” Romney said. “It demands and creates heroic souls.”

The former Massachusetts governor, who once served as a lay pastor in his Mormon congregation in Boston, said that speaking at Liberty University was a “great life honor.” He paid tribute to Falwell, who founded the school 41 years ago, by calling him a “cheerful, confident champion for Christ.”

Liberty alumnus Mark DeMoss, a longtime senior adviser to Romney on religious issues, sought to validate Romney’s Christianity with an introduction. DeMoss said that although he might not agree with Romney on everything, “I trust his values, for I am convinced they mirror my own.”

DeMoss recalled bringing Falwell and other religious leaders to meet Romney in Massachusetts in 2006, after which Romney sent Falwell a chair with a seal that said, “There’s always room for you at my table.” The founder’s son and school chancellor, Jerry Falwell Jr., sat on the chair during the commencement. And the school presented Romney with a chair of his own, saying, “There’s always a seat for you at our table.”

Six years ago, Sen. John McCain (Ariz.) made a similar pilgrimage to Liberty to build ties with Christian conservatives on his way to winning the 2008 GOP nomination. McCain had once referred to Falwell and other evangelical leaders as “agents of intolerance.”

For weeks, Romney’s advisers deliberated over how much the candidate should delve into strongly debated social issues or discuss his Mormonism at Liberty, which would make up the largest audience of his 2012 campaign. Ultimately, advisers said, Romney did not feel compelled to expound on his personal faith because he had already delivered a major speech on his Mormonism in December 2007, during his first presidential run.

“This isn’t a speech about Mormonism,” senior Romney adviser Eric Fehrnstrom told reporters before the address.

Although he never uttered the word “Mormon,” Romney did make a single oblique reference to his religion.

“People of different faiths, like yours and mine, sometimes wonder where we can meet in common purpose when there are so many differences in creed and theology,” Romney said. “Surely the answer is that we can meet in service, in shared moral convictions about our nation stemming from a common worldview.”

Romney’s Mormon faith is a sensitive subject on campus at Liberty, where each class opens with biblical devotionals and the curriculum refers to Mormonism as conflicting with the school’s Christian theology.

After administrators announced last month that Romney would be the commencement speaker, some students objected online and in the student newspaper, prompting Falwell Jr. to remind them that the school has invited non-evangelical speakers in past commencements, including conservative commentator Glenn Beck, who is also Mormon.

Some conservatives in attendance here who had supported Romney’s chief GOP rival, former senator Rick Santorum, said they had grown comfortable with Romney. They said he could appeal to evangelicals without delivering a partisan call to arms to the movement.

“You’re at a crowd where you already know we agree on social issues, so he doesn’t need to push that and spend time on that,” said John Campbell from Fayetteville, N.C., who is now supporting Romney. “We’re at Liberty, so we know where you stand if you come here. This school certainly has never run from its beliefs.”

But others in the crowd, which began assembling in the stadium at dawn, more than four hours before Romney spoke, said they were hoping to hear the candidate offer a strong defense of social conservatism — especially after Obama’s interview on same-sex marriage.

“We want God to bless our country, and I think we need to be moral,” said Lew Ann Knouse, 51, an office administrator from Altoona, Pa. “I’m against gay marriage, and people want to know Mitt Romney’s stand. He should let us know his social stands because if he doesn’t agree with the things I think are important, I’m not going to vote for him.”

Although Romney’s address was not billed as a political speech, he could not escape the intensifying general election campaign. A small airplane rented by liberal group flew over Liberty’s stadium with a banner that read: “GOP=Higher School Debt.”

Staff writer Krissah Thompson contributed to this report.