The door is a symbol of secrecy and avoidance, a symbol of the quiet or sad secret struggle of the mind hiding in bliss. A house without a door is not a house, but a hallway. Wherever a man is, he can make himself at ease as long as he is behind a closed door. The mind works most effectively in a closed door. People are not horses that graze together.
The correct interpretation of this paragraph is that people have thoughts and feelings, and they need to have their own independent world.