One issue which I am very interested in exploring is that of monotheism. When did monotheism first exist? Many people would quickly say that ancient Israel was a monotheistic people-group. The Hebrew Bible, though, says otherwise. Even in the Hebrew Bible we see evidence of Judeans and Israelites worshiping gods who are not Yahweh. Likewise, we have many inscriptions attesting to the existence and worship of other deities by Judeans. Some inscriptions reach back to the 10th century BCE. Finally, archaeological evidence from the region suggests that Yahweh was not the only god worshiped. 
We should likewise be cautious when assuming that early Christians were monotheistic. While they surely believed in one god, our category of monotheism still limits them. According to our category of monotheism, one is a monotheist if they believe in the existence of one god. Ancient Christian views of god, particularly that of gnostics, was more nuanced, though. David Brakke notes an important nuance to considering to when calling early Christians or Christian gnostics “monotheists”:
No ancient person (even one who was a Jew or Christian) was a monotheist in our sense, that is, someone who believes that one and only one God exists. Instead, ancient “monotheists” simply believed that a single High God stood atop a hierarchy of gods, daemons, and other spiritual beings. Neither were the Gnostics alone in their multiplication of divine aspects of the ultimate God. Christians such as Basilides and the Valentinians also imagined a complex godhead with multiple aeons.
Brakke, David. The Gnostics. Harvard University Press, 2010. EBSCOhost. Pp. 61-62.
In other words, monotheism existed; however, it was not understood in the way we understand it in the modern period. Monotheism still allowed for other gods, daemons, and spiritual being in antiquity. In Gnostic theology, everything came out of one primary deity. While a single deity was at the top of the ladder, there were other deities below him. Though lesser in power, they were arguably still deities.
 I am in the processing of writing a definition of Judean and Israelite Religion for Ancient History Encyclopedia. This is the basic outline for how I will attempt to “define” religion of the ancient Judeans and Israelites.