Before science explained things rationally for us, the world was buzzing with supernatural forces.
For the ancients, looking upward was to glimpse the divine heavens. For them it was as if the circular world was covered by an inverted glass bowl; the events in the sky, the weather, the passage and phasing of sun moon and stars were all played out at the level of the heavenly dome. They were so lofty and so wonderful--they must have meaning since everything had a 'spiritual' meaning. Life back then was as Thomas Hobbes said echoing Job: "short lived and brutish," there must be something better. The heavens are above the Earth, down here is the home where us poor mortals dwell and the heavens are the abode of the immortal gods-- then it would follow to look to the heavens for a sign!
You can after all predict the coming weather especially if you live outdoors, you become able to read the signs. By reading the position of the stars and the position of the sunrise and sunset by markers on the horizon, you can accurately say what time of year it is without a printed calendar-- and therefore know when to sow each of the different crops.
The heavenly canopy was not just predictive but also a source for universal folk myth. All children being taught these tales handed down through endless generations the things represented by the heavenly constellations. Being universally superstitious, these stories also were taken literally to predict divine revenge and cataclysmic change. The Bible perpetuated many of these sentiments by changing them from oral tradition to written text.
Today only superstitious people believe in prophecies.