Here’s a brief explanation of the subject of mythicism as it applies to Jesus and others. It is well known that, upon contact with the Greek culture as it spread east, into Persia, etc., during the first centuries surrounding the common era, many cultures began applying attributes of Greek gods and goddesses to their local deities. These cultures also increasingly depicted their deities as anthropomorphized, represented in art as human beings, as had been done by the Greeks, Romans and Egyptians in particular. In this way, their gods – mythical beings – while acquiring greater and more supernatural attributes also became further personalized, to the point where they were depicted as men and women having adventures on Earth.
The same process occurred with the Jewish god Yahweh, who acquired attributes from the Greek gods: For example, the Jerusalem temple was shared by Yahweh and Zeus during the reign of Antiochus IV Epiphanes (c. 215-c. 154 BCE). As this pantheon of anthropomorphized gods increased with the expansion of the Roman Empire, which reached from Great Britain to the Near East and included an enormous amount of deities, the Jewish priesthood (and others) did the same thing that everyone else was doing: It anthropomorphized its god, turning the long-awaited messiah of the Old Testament into “God’s son,” just as Zeus had a supernatural son, Hercules. This fictional Jewish godman then served as a “historical” competitor with these other gods, acquiring their various attributions, in order to reign supreme.
Hopefully, that explanation clarifies the process by which the mythical composite figure of “Jesus Christ” in the New Testament came to be. The mythical, spiritual and allegorical was made into the “historical,” not the other way around.