What kind of door is this?
Many colonial homes in New England have a feature called the Coffin Door. This door had only one function: allow easy access to the front parlor for the coffin containing the remains of a recently deceased member of the family. The door is also known as the funeral door, the casket door, or the death door. That last name makes one wonder if the expression, “being at death’s door” is associated with this feature.
Why this room?
In Colonial times, houses were built (mostly) on streets that ran either north/south or east/west. The front parlor of the house would be in the front on either the south/west corner or the south/east corner, depending on which side of the street the house was on. This room was chosen as the parlor because, especially in winter, it was where special guests were entertained. The room had more natural light and warmth from the sun, thus saving on candles and firewood. The door is on the side with the most sun exposure, entering directly into the front parlor.
In some houses, there is an inner door and an outer door. The inner door could be taken down and used in different ways: a platform upon which to put the coffin for transport into the parlor; a platform upon which to put the coffin during viewing; or, a table to hold refreshments served to those who came to pay their last respects.
The houses that lent themselves to having a coffin door are the ones with a large central chimney or central staircase. Either feature made it difficult to carry the coffin in the front door and make the turn into the front parlor.
Whose idea was this?
Pilgrims and puritans, most likely, brought the knowledge of this type of door with them from Europe. In the Netherlands, they called it a dodder (death door), and in Germany, they had the seelen fenster (soul/spirit window) which would allow the spirit of the deceased to escape.