She was responding to a question from a Conservative MP who asked the Prime Minister if she would endorse a recently published book called Speak Up (created by the Lawyer's Christian Fellowship and the Evangelical Alliance) which is designed to help readers understand what their rights are and what the law says in terms of sharing and practising faith in everyday British life.
There have been concerns among some Christians that currently laws, as well as counter-extremism measures by the government, restrict a believer's ability to share their faith or their views on certain issues like gay marriage.
The MP's question came after the chair of the Equality and Human Rights Commissioner, David Isaac, said earlier this week that British employers should fully embrace Christmas without fear of offending staff who do not celebrate it.
The PM told the House: "My honourable friend raises an important issue which matters to both her and me, and I think that the phrase that is used by the book was 'the jealously guarded principle' of that ability to speak freely... about one's religion. I'm happy to welcome the publication of this report and its findings".
"Of course, we're now into the season of Advent and we have a very strong tradition in this country of religious tolerance and freedom of speech and our Christian heritage is something we can all be proud of.