The relation of the astral body to the physical body, is like that of a workman to his machine, but with the difference that in this case the workman is in the machine, he ensouls the various parts, and makes them move. This resemblance of worker to machine applies even better when the person lies asleep. The astral body then works from outside. It makes good the damage suffered by the physical body during the day. So one can see the disadvantages for people who sleep badly.
Beings belonging to the third elemental kingdom have an influence on the astral body.
Beings belonging to the second elemental kingdom get at the etheric body and those belonging to the first elemental kingdom get access to the physical body to destroy it. Only when the astral body works on the physical body during sleep are these destructive processes made good. Just to know this does not have any influence. When however, a person begins to work on his spiritual development, he must also create the necessary conditions for the astral body to work upon the physical. Meditation influences the work of the astral body upon the physical and etheric bodies during the night.