"This way they are sharing their day with other people - people that will be companionable. It means such a lot to such a lot of people."
About 450 people have volunteered to lay tables, peel spuds and prepare meat for the lunch.
Despite that, the operation was nearly derailed a week ago, when a head chef could not been found.
A Herald On Sunday story on the dilemma attracted 70 volunteers - many with extensive restaurant experience.
Restaurant Association apprenticeship coordinator Peter Le Grice was this week picked for the role.
He will oversee the production of a menu that includes ham, chicken, roast potato and kumara, beans and carrots, with jelly and ice cream for dessert, followed by Christmas cake. Every diner will receive a Christmas gift.
Ms Robertson said she expected the event to run with "military" precision.
"It will just flow incredibly well.