"We're going to protect Christianity," he said. "If you look at what's going on throughout the world...Christianity is under siege."
Trump pointed to targeting of Christians by terrorist groups in Syria and urged Christians to work together to use their "power" within the United States to enact change.
He added that "I'm a Protestant. I'm very proud of it, Presbyterian to be exact. ...[but] bad things are happening, very bad things are happening."
The speech comes on Martin Luther King, Jr. Day, and Trump dedicated what he called a record-breaking crowd to the late civil rights leader.
The speech could give Trump a chance to strengthen his outreach to evangelical voters, whom he said he's doing "great with" in Iowa. He noted that he's heading to the early-voting state, as well as New Hampshire, after his speech on Monday.
"I want to win Iowa," he said. "Then we're just going to clean the table."
Trump got a warm introduction from Jerry Falwell Jr., the president of Liberty. While he noted the college doesn't endorse presidential candidates, Falwell said that Trump is a "breath of fresh air," "loves this country" and wants "more than anything to make America great again."
Trump, however, caught flack on social media after he called Second Corinthians, "Two Corinthians" when he referenced the book of the Bible made of Paul's Second Epistle to the Corinthians.
“Two Corinthians, right?” he said. “Two Corinthians 3:17. That’s the whole ballgame.”
The verse reads: "Now the Lord is that Spirit: and where the Spirit of the Lord is, there is liberty."
The slip comes after Trump called the Bible his favorite book last year, but wouldn't share
his favorite Bible verse. On Monday, he said it was the only book better than his No. 1 bestseller "The Art of the Deal."
He added that if he's elected president "you're going to see Merry Christmas in department stores. ...I have friends who aren't Christian — they like to say Merry Christmas."
Starbucks was the latest store to spark anger from evangelicals, who argued that the company's largely blank red holiday cup was part of a war against Christmas.