Echoing his mother's words in her last Christmas message, where she spoke of her grief at losing her husband Prince Philip, Charles said Christmas was "a particularly poignant time for all of us who have lost loved ones."
Thanking those who had sent "deeply touching" messages of condolence to him and the Queen Consort Camilla, he said the royal family had been shown "love and sympathy."
He also drew upon the late queen's "faith in God" and "faith in people," saying he shared it "with my whole heart."
Charles delivered his pre-recorded message standing in St George's Chapel in Windsor, where the queen and Prince Philip are both buried. Footage of the royal family, including Prince William and Princess Kate of Wales, appeared on screen while he spoke.
In a separate pre-recorded message broadcast to the nation as part of a Westminster Abbey carol service, the Princess of Wales said the royal family's first Christmas without the late monarch would "feel very different".
In his message, the king also paid tribute to the public sector and healthcare workers, charities and religious institutions, praising the latter for their work during the UK's ongoing cost of living crisis.
He ended his speech by referring to a previous visit to Bethlehem, the town where Jesus was born, and "the power of light overcoming darkness."
"It is in this life-giving light and with the true humility that lies in our service to others that I believe we can find hope for the future," Charles said. "Let us, therefore, celebrate it together and cherish it always."
His message ended with a rendition of 'O Little Town of Bethlehem,' which Charles used to cite the late queen's "belief in the power of that light," performed by the choir of St George's Chapel.
Reuters