Imam As-Sadiq (‘as) said:
Self-acknowledgment is realized through four natures, four supports, and four pillars. The natures are blood, bile, wind, and phlegm. The supports are intelligence parts of which are understanding and maintenance.8 The pillars are light, fire, soul, and water. The feature of man is his nature. He could see through light, eat and drink through fire, copulated and moved through the soul, and found the taste of every tasted thing and food through water. This is the basis of man’s feature. A man whose intelligence is supported by light becomes knowledgeable, retainer, clever, shrewd, and thoughtful. He should also recognize the real situation that he is in, the source of his situation, the reason beyond his existence, and the fate that he will inevitably encounter, through the sincere belief of God’s oneness and the submission to the obedience (to Him).
The soul may move in him with its heat or coldness. When heat of the soul influences that man, he will behave evilly and arrogantly, feel comfortable, kill, rob, feel pleasant and dashing, commits sins and fornication, and spend lavishly.
When the soul covers that man with its coldness, he feels depressed, sad, submissive, withered, and oblivious. These are the symptoms that cause diseases. This coldness is originated only when the individuals commit a sin and have a drink or food in an hour that is not appropriate to that drink or food—all in the same time; therefore, this will create a certain pain.
Imam As-Sadiq (‘as) explained the topic in other words. He said:
Man drinks, eats, and works through the fire; hears and smells through the wind; enjoys the taste of food and drink through the water; moves through the soul. Food and drink cannot be digested in the interior body without the existence of the fire in the stomach. Without the existence of the wind, the fire of the stomach cannot be flamed and the dregs cannot find an exit out of the abdomen. Without the existence of the soul, man cannot come and go, i.e., move. Without the existence of the cold water (in the stomach), the fire of the stomach would burn (man). Without the existence of light, man cannot sight or understand. Clay is his nature. The role of bones in the human body is as same as the role of trees on the surface of the earth.
The hairs on the skin play the same role of the grass on the earth. The nerves of the human body play the same role of the bark on trees. The blood of the human body plays the same role of water on the earth. The earth cannot endure without water. In like fashion, the human body cannot endure without the blood. The brain is the fat and the foam of blood.
This is the human being who was created from matters of this world and matters of the world to come. If God combines these matters, man’s life will be on the surface of the earth, because he descended from the matters of the heavens to the world. When God disconnects these matters by means of death, the matters of the heavens go back to their source; the heavens. The life is on the earth and death is in the heavens by means of separating the soul from the body.
The soul and the light are taken back to the foremost power and the body is left, because it is composed from matters of the world. The body disintegrates in this world because the wind dries water and the clay becomes debris and old and return to its first core. The soul moves in the breath whose movement is out of the wind. The breath of the believers is light that is supported by the mind while the breath of the disbelievers is fire that is supported by devilry. This is the nature of its fire and the earlier is the nature of its light. Death is God’s mercy from the believers and God’s punishment on the disbelievers.
God has two punishments; the soul is the source of one and people’s predomination on each other is the source of the other. Ailment and poverty are the punishments whose source is the soul while agony is the punishment whose source is people’s predomination on each other. This is indicated in God’s saying:
Thus, do We make the unjust ones predominate one another because of their evil deeds. (6:129).
These evil deeds are their sins.
The punishment of the sins whose source is the soul is ailment and poverty, while the punishment of the sins the source of which is people’s predomination on each other is the agony. All these are punishment and agony for the believers in this world. For the disbelievers, these are punishment in this world and harsh agony in the world to come. The reason for any punishment is a sin and the source of every sin is passion. The sins of the believers are flaws and matters of oblivion or compulsory and unendurable. For the disbelievers, their sins are intentional, denial, aggression, and envy. This is indicated in God’s saying:
Once you have accepted the faith, many of the People of the Book would love, out of envy, to turn you back to disbelief, even after the Truth has become evident to them. Have forgiveness and bear with them until God issues His order. God has power over all things. (2:109).