"John McCain has an innate sense that using your faith for election is wrong and that his faith is extremely private," said a McCain religious advisor, who wanted to remain anonymous, to David Brody of the Christian Broadcasting Network.
"He is not someone who feels comfortable expressing it on the campaign trail and I think a lot of it has to do with the feeling that he's using it for public gain," the source added. "I'm not saying he won't discuss his faith in public forums. Is he going to do it? I don't know."
McCain has kept a low profile when it comes to "God talk", despite the prominent role religion has played in this year's presidential race.
Both Democratic candidates Senators Barack Obama and Hillary Clinton have participated in forums hosted by Christian organisations and candidly spoken about the influence that faith has on their political decisions.
Last fall, Clinton spoke at a HIV and church conference hosted by Pastor Rick Warren and his wife Kay at Saddleback Church, while Obama held a series of gospel concerts featuring Grammy-award winning Christian artists ahead of the North Carolina primary.
Meanwhile, McCain's former Republican presidential rival, Governor Mike Huckabee, is an ordained Southern Baptist preacher who frequently weaved Bible passages and references to God and faith in his stump speeches.
But McCain has remained rather mum on his faith. He is officially an Episcopalian but has attended a Baptist church for some 20 years.
This past weekend, McCain declined to attend the high-profile Compassion forum - which featured Clinton and Obama discussing their faith and moral issues. But the source explained that the McCain campaign saw the forum as more of a Democratic event - it took place nine days before the Pennsylvania primary - and would likely attend another similar event in the fall.
Beliefnet.com's "God-o-Meter" - which measures a candidate's rate of God-talk and effectiveness - gives Clinton a 9, Obama an 8, and McCain a 4 out of a possible 10 points.
However, the campaign insider is unconvinced grassroots activists are requesting to hear McCain speak more about his faith.
"I'm not completely convinced that John being forced to talk about his faith is the thing that he needs to do," the source said. "Maybe he will someday if that's something he feels called to, because John McCain doesn't do things he doesn't feel called to."
Regarding the Democratic candidates' appeal to faith voters, McCain's religious advisor said evangelicals and Christian voters are not going to ignore the abortion and gay "marriage" issue, which will cause them to differ with Clinton and Obama.
The source contends that Christian voters will look for a candidate that offers the "full package," and only McCain represents their view on abortion and traditional marriage while also taking on Darfur, poverty and other humanitarian efforts taken up by Christians.
