God created man in His own image, breathed into him the breath of life, and man became a living soul. Man was created with a triune nature of body, soul, and spirit. The body is the physical part of man. The soul and spirit are the spiritual parts which enable him to act, think, feel, react emotionally, and spiritually respond to God. Originally, each part of this triune nature was in harmony with the other two, and the entire triune nature of man was in harmony with God. Man was sinless and healthy in body, soul, and spirit.
Genesis, Chapter 3, records how the first man and woman, Adam and Eve, sinned against God by disobeying His Word. Their sin brought the curse of sin and death upon all men.
“Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned:” Romans 5:12
This curse of death was a spiritual separation between man and God, as well as physical death, which would end mankind’s life.
We can see the effects of the curse immediately in the Genesis record. Adam and Eve hid from God because of the spiritual sickness of sin. Adam blamed Eve, which is the start of emotional sickness that results from disintegrating relationships. Cain killed Abel, which is an example of social sickness. Physical sickness, which ultimately leads to death, enters the record through the barrenness of Sarah and the plague upon Abimelech.
When the curse of death came upon mankind, Satan entered the genetic system of the body to begin his destructive mission. The Bible confirms that Satan is the source of evil in the world. Jesus said that Satan is a thief. The thief cometh not, but for to steal, and to kill, and to destroy … (John 10:10). Sickness destroys the body like sin destroys the spirit. Disease steals health, happiness, money, time, effort, and strength. It truly kills and destroys. Even accidents that harm the body are destructive agents of Satan.
Because the source of sickness is Satan, you must resist it, as you resist temptation and sin. When you resist temptation and sin, you are doing spiritual warfare against Satan’s attacks on your soul and spirit. When you resist sickness, you are waging spiritual warfare against his attacks on your physical body.
Every disease comes from a germ of life. As your spirit gives life to your body, Satan provides the destructive elements of sickness. In the natural world, God takes a living cell, multiplies it to bring forth life, and a new child is born. Satan counterfeits this positive process with a negative one of his own. He takes a living cell (virus, cancer, etc.) and multiplies it to bring forth death. This is the spirit of infirmity which works within your body when you are sick. When the spirit of infirmity is cast out, disease in your body dies. As long as that germ exists in a body, the disease lives and continues its destructive work.
Although every disease is not a direct attack of demonic spirits, the elements of sickness exist in the world because of Satan. For example, you might catch a cold because you went barefoot in freezing weather. This is not a direct attack of demonic spirits, but the elements of sickness that resulted in your cold exist because of Satan.