Today we think of a threshold as the beginning of something or that block of wood under your front door. The origin of the word threshold came about in an attempt to solve a household problem.
Back in the day before hardwood floors or carpeting, the floor in home dwellings was simply dirt. Farmers discovered that they could use the stalks of wheat left over after the threshing process to put on the dirt floor to keep the dust and mud down.
Threshing is the process of separating the edible part of grain or other crop from the stalk. Farmers scattered the leftover stalks around the dwelling. The problem was that the stalks or thresh would tend to slip out under the front door. The farmers found that if they installed a block of wood under the front door it would hold the thresh in the house. Thus was created the threshold.