Very many years ago primitive humans looked at what happened; some things were done by humans, animals and/or plants, and also others by what we now call nature, but was then PROOF that God or gods or some other spirits exist that did all those "other" things. Such as the growing of things, the weather, the movement around the Earth of the sun, the moon and all of the stars, perhaps they included also a belief that the puddles after a rainstorm were gradually getting smaller because the gods were drinking that water. They had PROOF and proceeded to try to influence those with important influence. Apparently early believers actually thought that God was very much involved in human matters, and lots of speculations by clergy and others were later assumed to be "Gospel truth" by many others, or even handed down items from their deity.
..... Summing up, religion now is based on faith, but long before Science existed religion was based on what was then thought to be PROVEN FACTS.