The film has been released ahead of the wedding of Prince William and Kate Middleton next Friday, which the Archbishop will be conducting.
"Any priest or minister conducting a wedding is bound to feel a huge sense of privilege," he says in the film.
"You're invited into some intimate places in people's lives. You're invited to take part in a very significant moment, a moment of hope; a moment of affirmation about people's present and future.
"And I've felt very privileged to be part of this event for those reasons. Here are young people sending a message of hopefulness, sending a message of generosity across the world.
"And it's my privilege to be able to bless that in the name of God, to witness it in the name of God."
The Archbishop goes on to say that he has been "very struck" by the way in which the couple have approached their marriage.
"They've thought through what they want for themselves, but also what they want to say," he says.
"They've had a very simple, very direct picture of what really matters about this event.
"I think that they have a clear sense of what they believe they're responsible to.
"They're responsible to the whole society; responsible to God for their relationship. And I think it's impressive that they've had that simplicity about it, they've known what matters, what's at the heart of all this ... because I think they are deeply unpretentious people"
The Archbishop concludes by urging all those who will be watching on the day to offer their support and prayers to the couple as they take this significant step.
"William and Catherine are making this commitment very much in the public eye and they're sensible, realistic young people," he says.
"They know what the cost of that might be. They've thought that through. And because of that they will need the support, the solidarity and the prayers of all those who are watching today.
"We have to be witnesses in an active sense: the kind of witnesses who really support what's going on. To be a witness is more than to be a spectator and I hope that'll be part of people's experience at the time of the wedding."
The short film is available to view on the Archbishop's website at www.archbishopofcanterbury.org