Religion, Preliminary Research for Studying the History of Religions

Talking about human beliefs is essentially an old matter; Contemporary - because people differ in their sects and approaches - its material expands at times and narrows at times; To the extent that people of religions get to know each other and agree with each other's doctrines. Its character and direction also vary, keeping pace with the diversity of researchers' tendencies and goals.
If we follow the series of talk about religions from the era of the Pharaohs, then Greece, then the Romans, then Christianity, then Islam, then the modern renaissance; We would have been able to discern the difference in its forms between era and era, and perhaps even between period and period, from the periods of one era.