Today, crossing the threshold signifies a figurative beginning.
But a thousand years ago, a threshold was just the floorboard in the doorway of a country cottage.
Threshing is the process of separating wheat from the straw.
While the wheat was stored, straw, among other things, was used to cover both slate and dirt floors.
The board in the doorway that held the straw inside was called the threshold, holder of the straw.