3000 B.C.: The baru will predict your future

Divination is the interpretation of omens or signs to predict the future.  Most ancient societies, from Ancient Greece, Ancient Egypt, Ancient Mesopotamia, Ancient India, Ancient China and Ancient Rome all believed in omens.  And there were good and bad omens.  (1,2)

You are sick.  You have sinned.  You are impure.  You are in disharmony with the world.  You are a burden on society.  You are unclean.  So you go to see a healer; a priest. Since disease, your symptom, is caused by magic, you need a magic remedy.  The healer gives you an incantaion.  He also, if you can afford it, can use divination to learn how you got sick and how to heal you. 

Through divination he can give you hope, which modern studies have proven, can help you get better.  Optimism heals.  Or he could predict that your ill health is futile and that you will die, and in that case fill you with gloom and pessimism.  He could predict success in wartime, and inspire soldiers.  Or he could predict a loss, and therefore cause resignation among soldiers. 

The priest who did this were the baru, the diviner.  They are specially trained in the divination.  They may ask you questions:  Did a bird cross your path.  If it did, was it to the left or right.  If you saw birds flying to your left when you broke your foot the birds brought back luck.  This was no coincidence.  You are cursed.  The remedy is to chant this incantation or to put this amulet on a chain around your neck, or over your doorway or window.(2)

There were other means of getting omens, depending on how much you can afford.  Probably the most expensive, yet most revealing, would be to have a baru examine the liver of a sacrificed animal by Babylonian baru. 

By studying the liver, most often by sacrificed animals such as sheep, the baru could learn much about the future.  According to Henry Osler in his series of lectures at Yale University in 1913, "Of all the organs inspected in a sacrificial animal the liver, from its size, position and richness in blood, impressed the early observers as the most important of the body.  Probably on account of the richness in blood it came to be regarded as the seat of life --- indeed, the seat of the soul." 

The liver to the Babylonians is similar to the heart to the modern world:  it's the soul  of life; the center of vitality  "Hepatoscopy," Osler states, "thus became, among the Babylonians, of extraordinary complexity, and the organ of the sheep was studies and figured as early as 3000 B.C.  In the divination rites, the lobes, the gall bladder, the appendages of the upper lobe and the markings were all inspected with unusual care."

Readings:  gallbladder... liver....

Cheaper methods would be to drop oil over water and watch what happens.  Or a flame was lit and the flickering was examined, conclusions drawn.

Knowledge that the baru had was esoteric.  Many religious texts ended in "May he who knows instruct him who knows.  And may he who knows not read this."  And "He who does not keep the secret will not remain in health -- His days will be shortened." (2, page 433)

References:

1. Osler, William, "Evolution of Modern Medicine: a series of lectures at Yale University to the Silliman Foundation in April 1913, 1921", New haven, Yale University Press, pages 18-19
2. Sigerist, Henry E., A history of medicine," 1955, 2nd edition, volume 1, pages 453-5, 433