On Wednesday, the father-of-five will baptise Prince William and Kate Middleton's baby son at St James's Palace. The ceremony, he says, will mark the next "hugely important moment" in the little Prince's life, following his birth on 22 July.
"We celebrate, first of all, the joy of the parents," he said. "It's a wonderful thing, having a baby. All babies are unbelievably special, not only royal babies.
"As a nation, we're celebrating the birth of someone who in due course will be the head of state. That's extraordinary.
"It gives you this sense of forward looking, of the forwardness of history as well as the backwardness of history, and what a gift to have this new life and look forward."
Mr Welby, a former oil executive, said that new parents William and Kate have probably already been given as much advice as you could "fill a house with" — but he offered them some words of wisdom.
"My message to them would be — what a treat, what an amazing gift, what wonderful times that you will have.
"There'll be great times and tough times — there always are with children.
"Through christening you're bringing God into the middle of it all, and I know that when he's in the middle of it all somehow it's held in his hands, and that's extraordinary."
Prince George will be baptised by the Archbishop at 3pm on Wednesday 23 October.
The intimate service, which will be held at the Chapel Royal, St James's Palace, will last approximately 45 minutes, and will be attended by close family and the baby's godparents.