Theresa May was responding to a question from the Conservative MP for Congleton and Christian Fiona Bruce, who asked the Prime Minister if she would endorse a recently published book called Speak Up.
Speak Up was created by the Lawyer's Christian Fellowship and the Evangelical Alliance.
It's 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.
Fiona Bruce's question comes 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.
Responding to the MP's question, Theresa May told the House of Commons: "My honourable friend raises an important issue which matters to both her and me, and I think that the phrase that was used by the Lawyer's Christian Fellowship 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.
"I'm sure we would all want to ensure that people at work do feel able to speak about their faith and also feel able to speak quite freely about Christmas."
