David Cameron has urged people to reflect on Britain's Christian values in his Christmas message.
The PM said the country's "important religious roots" made it "a successful home to people of all faiths and none".
Labour's Jeremy Corbyn used a newspaper article to highlight homelessness and praise emergency workers.
Green Party leader Natalie Bennett called for a "different sort of society" while Lib Dem Tim Farron said the world was "in need of hope".
Mr Cameron highlighted the plight of people spending Christmas in refugee camps having fled the civil war in Syria, while Christians in some parts of the world would go to church in fear of persecution.
"Throughout the United Kingdom, some will spend the festive period ill, homeless or alone," he said.
'Make a difference'
He paid tribute to people working at Christmas "to help the vulnerable" and said the armed forces were "in the skies of Iraq and Syria, targeting the terrorists that threaten those countries and our security at home" as well as saving migrants attempting to cross the Mediterranean.
"It is because they face danger that we have peace," he added.
Labour said Mr Corbyn would not issue an official Christmas message, but in a Sunday Mirror article, he said many low-paid workers could not afford to take time off over Christmas, and that homelessness was increasing with tens of thousands of people spending the festive season in temporary accommodation.
People should ask themselves whether they could do more for others, he said.
"Jesus said: 'It is more blessed to give than to receive'", he said.
"It is a similar maxim that inspired our party: 'From each according to their means, to each according to their needs.'"
Ms Bennett said people should look to 2016 "with the understanding that politics shouldn't be just something that gets done to you.
"Politics should be something that you do to make a difference in your society."
Mr Farron said he hoped people would be inspired in 2016 to make the country a more "compassionate, liberal and welcoming one", Lib Dem Voice reported.