A Lammas Bannock was made from the grains that had been newly harvested.
Later Lammas Bannock became a loaf of actual bread made from the first grains harvested. Lammas Bannock would be either given as a gift to the local clergy, or taken to Church to be blessed and brought home to have as part of the meal that day.
Eventually the Lammas Bannock became the Marymas Bannock.
Language Notes
In Scottish, Lunasagh was called “lunastain” and Lammas Bannock was “bonnach lunastain.” In English, Lammas Bannock got called “Loaf mas”, after the bannock that was made from the first grains.