All doors were to be shut gently, noiselessly, at all times. When a door is shut, one can but imagine what goes on beyond. An open door extends one's sight into the vista beyond, be it out into the world or in into a room. Through an open door, a room once hidden assumes a reality which was otherwise held up only by remembrance, or imagination, or faith. Doors have this power of magic.
Doors hold every shape and every rank.
As an extension of human capability and complexity, doors may not rank with other technology such as the telephone, computer or automobile. However, as low-tech and very simple machines, doors are ubiquitous. They are found in every facet of virtually every human community, representing a binary boundary - open or shut.