"have the banns published immediately"

Certificate of Proclamation of Banns
Creative Commons AttributionCertificate of Proclamation of Banns - Credit: Flickr user crabchick

Banns serve to announce that an engagement has been set and a marriage is going to take place. Banns were announced several weeks leading up to the proposed wedding so that any impediments to marriage could be discovered before the event was scheduled to occur. By having the banns published, Grace is acting on faith that Robbie will return unharmed and the wedding will proceed as planned.