Limbaugh? You might want to look that up yourself.
This is from the text of Romney's speech:
"In John Adams' words: 'We have no government armed with power capable of contending with human passions unbridled by morality and religion... Our constitution was made for a moral and religious people.'"
"Freedom requires religion just as religion requires freedom. Freedom opens the windows of the soul so that man can discover his most profound beliefs and commune with God. Freedom and religion endure together, or perish alone.
Only the first part of that is Adams (the actual quote is more obvious in the written format). The rest is Romney. Limbaugh is wrong on this. I like Rush, but he's one of those sources you always need to check on for yourself.
The complete source of the Adams quote is here.
Adams was not a deeply religious man, and did not hold with a lot of Christian theology, but he was a believer in an overriding moral principle that underlies all good government. His point here is that a free society requires a moral cultural foundation to survive, of which only one aspect could be religion. It means that if we abandon morality, honor, and other basic virtues in America, political and economic freedom isn't going to last much longer past that.
The corollary is that you aren't going to make a nation free simply by implanting a Constitution and elections on it if the underlying culture is still totalitarian or collectivist. We've been learning this the hard way in places like Russia. And yes, Iraq.