Gingrich, who is considering a 2008 presidential run, quoted Bible passages to a mournful crowd of about 17,000 packed into the university's football stadium four days after Falwell's death.
Despite the somber tone of the day, graduates who covered the football field chanted "Jerry! Jerry!" in tribute to Falwell.
"A growing culture of radical secularism declares that the nation cannot profess the truths on which it was founded," Gingrich said. "We are told that our public schools can no longer invoke the creator, nor proclaim the natural law nor profess the God-given quality of human rights.
"In hostility to American history, the radical secularists insist that religious belief is inherently divisive and that public debate can only proceed on secular terms," he said.
Liberty's commencement has become a forum for conservative politicians. Last year's address came from Republican presidential candidate John McCain, who made amends with Falwell after attacking him by name during McCain's failed 2000 White House bid.
Gingrich said he won't decide until October whether to run for president.
It was the first commencement without Falwell, the Baptist preacher who established the church-based university in 1971, before he founded the Moral Majority that helped elect Ronald Reagan president in 1980.
On Tuesday morning, the 73-year-old Falwell was discovered without a pulse in his office at Liberty and pronounced dead at a hospital about an hour later. His physician said Falwell had a heart condition and presumably died of a heart rhythm abnormality.
His funeral was set for Tuesday.
His son, Jerry Falwell Jr., addressed Liberty's students Saturday as the school's new chancellor.
"No one can replace dad, but ...," he said before he choked with emotion. Applause rippled across the crowd as he struggled to regain his composure. "But there's a team here ready to carry on and we're going to give it everything we have as he did for so long."
Falwell intended Liberty to be his most enduring legacy. He envisioned it as a "Protestant Notre Dame," projecting fundamentalist Christianity for generations. It was to be a training ground for conservative politicians, lawyers and judges — warriors in what Falwell perceived as a cultural war against liberals, gay rights, legalized abortion and forces he saw as a threat to Christianity.
Gingrich said after his speech that Falwell's death would not slow the Christian right's efforts.
"Anybody on the left who hopes that when people like Reverend Falwell disappear that the opportunity to convert all of America has gone with them fundamentally misunderstands why institutions like this were created," Gingrich said.