The Most Rev Justin Welby said people should not judge the monarch on her “external” appearance at the service, adding it would be an “anguished moment” for her.
Speaking to the BBC, he said: “We really have to avoid judging from anything external. She is the Queen She will behave with the extraordinary dignity and extraordinary courage that she always does.”
The funeral will be attended by just 30 guests due to coronavirus restrictions, and social distancing rules mean the Queen will sit alone.
Mr Welby, who will give a blessing during the service at St George’s Chapel in Windsor, said people of all faiths should show sympathy to the Queen after losing her husband of seven decades.
He said: “She is saying farewell to someone to whom she was married for 73 years.
“I think that must be a very, very profound thing in anybody’s life and I hope the whole nation, if they believe in that, they pray for her, and if they don’t, they sympathise in their hearts, offer their condolences to her and they hope for her to find strength in what must be an anguished moment.”
Philip will be interred in the royal vault in the chapel at the end of the service, which will be conducted by the Dean of Windsor, David Conner.
Buckingham Palace said the Queen faced “some very difficult” decisions as she selected the limited number of guests allowed to attend, and had tried to ensure all branches of the duke’s family were there.
Guests will include all of Philip’s children and grandchildren plus their spouses, the children of the Queen’s sister Princess Margaret, and three of Philip’s German relatives: Bernhard, Hereditary Prince of Baden; Prince Donatus, Landgrave of Hesse; and Prince Philipp of Hohenlohe-Langenburg.
Also invited is a close friend of Philip’s, the Countess Mountbatten of Burma, Penelope “Penny” Knatchbull, who was previously known as Lady Romsey and later Lady Brabourne, and was the duke’s carriage driving partner.