Speaking from London's Westminster Abbey, a day before "Royal Carols: Together At Christmas" was pre-recorded on December 8, the Duchess also recognised "those whose struggles perhaps have been less visible".
"We have been through such a bleak time. We have seen so many challenges. We have lost our loved ones. We have seen our frontline workers under immense pressure, and also we have been more emotionally and socially distanced and isolated from each other," she said.
"But I suppose through that separation, we have also realised how much we need each other and how acts of kindness and love can really bring us comfort and relief in times of distress," she added.
The message was recorded during a visit by the Duchess to the Abbey to help with preparations, including decorating Christmas trees donated by Britain's Queen Elizabeth from Windsor Great Park and arranging wreaths that were donated by the Royal Horticultural Society.
Led by the Duchess and supported by the Royal Foundation, the "Together At Christmas" carol service was attended by unsung heroes from across the UK in recognition of their inspirational efforts to protect and care for those around them, according to Kensington Palace.
"Royal Carols: Together At Christmas" airs at 7.30 p.m. local time (1930 GMT) on Christmas Eve on British television station ITV.