Given that it’s one of the building blocks of civilization, it’s not hard to see how fire became used in divination. Known as Pyromancy, this technique arose independently across many parts of the world.
In ancient Greece, fire was a godly element that was bestowed by higher forces. It’s said that followers of Hephaestus, the Greek god of fire and the forge, practised pyromancy. But before you go burning down a building just to find out your fate (probably jail), it’s best to start small with the flame from a candle and interpret the shapes you see within them. There are, of course, variations - alomancy, for example, involves casting salt into a fire, while botanomancy involves burning plants.