Donald Trump has warned that Christianity is "under siege".
In a speech today to evangelical Christians at Liberty University in Virginia, he quoted the Bible and pledged to protect the religion.
"2 Corinthians 3:17. Now the Lord is the Spirit... is that the one you like?" he said to his audience of thousands.
He continued: "We're going to protect Christianity. We don't have to be politically correct about it. They're chopping off heads in Syria. Christianity is under siege. I'm Protestant, Presbyterian, and I'm proud of it. Other religions frankly are banding together, we need to band together."
He said he had broken the record for crowds at the venue. On the day that the US was celebrating Martin Luther King Jr, Trump dedicated his speech to the civil rights activist.
He said: "If I'm president, you're gonna see 'Merry Christmas' again!" The crowd chanted back: "We're making Christmas great again!"
Jerry Falwell Jr, the Chancellor of Liberty University and son of televangelist Jerry Falwell who founded Liberty, praised Trump as someone who lives a life of loving and helping others.
He said that once when Trump's car broke down and a couple stopped to help him, he thanked them by paying off their mortgage.
Mr Fallwell said: "By their fruits shall you know them. Donald Trump's life has born fruit in jobs and generosity. He cannot be bought. He is not a puppet on a string like other candidates."
Earlier, in an interview with CNN, the Republican frontrunner said his wild days when his marriages and exploits would generate hundreds of words in newspaper gossip columns are firmly in the past.
He said he now enjoys a "very great relationship with God" and "a very great relationship" with the evangelical Christian voters who are crucial to campaigners in Iowa.
He said: "I live a very different life than probably a lot of people would think. I'm talking about over the last number of years, I'm leading a very good life. I try to lead a good life and I have."
He said he believed this was the reason he was doing so well in Iowa, where Ted Cruz and Trump are leading in the polls.
Trump, an opponent of same-sex marriage, married his third wife, Melania, 11 years ago.
He said: "I've had – actually I have a great marriage, I have a great wife now. My two wives were very good. And I don't blame them, but I was working, maybe like you, 22 hours a day. I blame myself because my business was so powerful for me. I don't know if that is a good thing or a bad thing."
He has said in the past that the Bible is his favorite book and once referred to Holy Communion as "my little wine and my little cracker."
MPs in Parliament are today debating a petition calling for Trump to be banned from entering Britain in the light of his remarks that Muslims should be banned from entering the US.