Man gains interest in the physical world through perception or estimatio. It's this interest that fetters him to the physical world. One can grow out of this by seeing the spiritual behind things in the sense world. In an earlier stage of consciousness men had imaginatio and no estimatio for physical things, and even earlier they had incantatio or inspiratio. Moderns usually only have estimatio during the day, and they have imaginatio at night. Men are unproductive in daytime; they used to be much more productive. Moderns are only productive during sleep. Consciousness arises when the astral body and ego destroy the physical and etheric bodies during the day. When the astral body and ego become aware of their physical surroundings it's as if the nerves were being torn to pieces.
Corporeal tiredness arises from the destructive, deadly effect of the astral body and ego on the etheric and physical bodies. The streaming of the physical world into man's organism has a poisonous, destructive effect.
At night the ego and astral body take in the forces of the spiritual world and stream them into the physical and etheric bodies. They surround the physical body with pictures that have a healing effect on it. The first thing a man sees when the spiritual world opens before him for the first time is his physical body. This picture of the physical body has a healing effect on him. Likewise the astral body and ego work upon the rest of man in a strengthening, healing way at night through true pictures out of the spiritual world. They stream into the ripped nerve strands and destroyed organism. Thereby forces from the spiritual world stream in at night that eliminate tiredness from the body.
Tiredness mainly arises from interest in things. No tiredness is caused if one looks at something without personal interest. For instance, say someone really likes a tasty food. Thereby he has a personal interest in the food because it stimulates his gums. It has quite a different effect on a man if he knows his connection with the cosmos and that he's at a stage where he has a physical body that needs food. This affects his organism differently than if he only eats food for pleasure. A man must get to know spiritual things through the physical body, and then he loses interest in physical things.
A man should look upon estimatio as the low point in evolution. He must grow out of this into the imaginatio that he had previously. But if he connects himself with the physical world he goes below the lowest point and can no longer ascend. It's very important for a man to learn to occupy himself with things that lie beyond the physical plane, with ideas and concepts that are super-sensible. Exercises are given to this end. The longer and more patiently a pupil practices certain ideas, the more he learns to overcome personal interests and to ascend to imaginatio. Then a man becomes productive instead of just taking in things from outside. He then streams something from within out into the world. One rightly says that man has the sun and moon in him. When he looks at things without personal interest he streams a spiritual light onto them; he becomes a sun who illumines things. They reflect his light. The surroundings that reflect his light become a moon.
Correct ideas have a healing effect on man, and wrong ideas make him sick. One can find a wrong idea behind every disease, if one traces it back. Mankind in general is responsible for this and not individuals. Interest also has a destructive effect when people run from one sensation to the other and always want to be amused. That makes people sick. It's also a hindrance to progress to have a personal interest in higher knowledge. Men become scleroticized thereby. A man must not become indifferent to his surroundings. He must retain his feeling and sympathy for his surroundings. Some say that sympathy can also come from egotism. That may be the case. Many kinds of sympathy only arise because one doesn't want to see other people suffer. That's even a good thing. It's better for a man to help someone out of egotistical sympathy than not to help him at all. But we must learn to develop a sympathy that stands above egoism, that helps neighbors because it's one's duty to help them.