Catherine, Princess of Wales, is presiding over her yearly Yuletide celebration at the iconic London venue, with a congregation comprising royals, celebrities and local heroes who have helped their communities.
The large audience will enjoy a mix of festive songs, musical performances, and spoken word pieces from stars like Kate Winslet and Chiwetel Ejiofor.
The focus of the event, held in the atmospheric historic church on Friday, is kindness and showing love to others.
In the audience are Jonathan and Anna Cordiner, whose daughter died of a tumour, and who established a foundation, a support fund, to support families who have a terminally ill child.
"Your efforts, love, and understanding, often without fanfare or recognition, and without any expectation or recognition, make an extraordinary difference to the circumstances of individuals," Her Royal Highness stated in a letter ahead of the concert.
The Princess of Wales is continuing her own steady comeback to public life following her health challenges and treatment, last month delivering her initial major address in two years, in which she reflected on recognising the "selfless, commonly overlooked efforts of carers".
Guests arriving at the Abbey can listen to young musicians aided by the Future Talent charity, established in part by the late Duchess of Kent to increase availability of instrumental training.
An 18-year-old named Carys Wood, who plays the trumpet and is from Wales, has been supported by the trust, with awards contributing to instruments, tuition, and transportation expenses - and she said it was "incredible" to be playing at the concert.
"Musical pursuits are frequently pricey," Carys said. She is now enrolled at the prestigious music academy, and added that "all people deserve the chance" to cultivate their performance abilities.
Eliza, Carys's sister who is 11, who is a euphonium player, will be present at the Abbey. "It's unbelievable that I get to perform here in front of so many notable figures," she said.
Attending the service will be representatives of different generations.
That will include nine-year-old Saphia Turner, honouree of a youth community award, who produces drawings and undertakes charity feats to generate funds for local food charities.
The Abbey has been festooned with custom-created holiday decorations, with well-known chef Mary Berry and flower expert Simon Lycett helping to make them.
Taking to the stage will be Katie Melua, choristers from Westminster Abbey and a nautical singing ensemble, the group Fisherman's Friends, who said the invitation to sing was "the perfect culmination."
The Together at Christmas carol concert will be broadcast on television on December 24th.
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