The same way every culture creates a religion. They come out of a society and borrow those ideas and combine them with societies they have moved closer to.
This is what we see. The monotheism was from Egypt. There were a few different Gods who for a time were the only supreme God.
God vs. the Gods - The First Known Instance of Monotheism in History - The Vintage News
They moved near Canaan so they adopted some of their deities.
"
According to the current academic historical view, the origins of Judaism lie in the
Bronze Age amidst polytheistic
ancient Semitic religions, specifically evolving out of
Ancient Canaanite polytheism, then co-existing with
Babylonian religion, and syncretizing elements of Babylonian belief into the worship of
Yahweh as reflected in the early
prophetic books of the
Hebrew Bible.
During the
Iron Age I, the Israelite religion became distinct from the Canaanite polytheism out of which it evolved. This process began with the development of
Yahwism, the
monolatristic worship of
Yahweh, one of the Canaanite gods, that gave acknowledgment to the existence, but suppressed the worship, of the other Canaanite gods. Later, this monolatristic belief cemented into a strict
monotheistic belief and worship of Yahweh alone, with the rejection of the existence of all other gods, whether
Canaanite or foreign."
The works you are familiar with are more modern 2nd Temple Period when they were changing to worship only Yahweh because they thought Yahweh was pissed about the other Gods and hence endless invasions -
"
During the
Babylonian captivity of the 6th and 5th centuries BCE (
Iron Age II), certain circles within the
exiled Judahites in Babylon refined pre-existing ideas about their Yahweh-centric monolatrism,
election,
divine law, and
Covenant into a strict monotheistic theology which came to dominate the former
Kingdom of Judah in the following centuries.
[1]
From the 5th century BCE until 70 CE,
Israelite religion developed into the various theological schools of
Second Temple Judaism, besides
Hellenistic Judaism in the
diaspora. Second Temple
eschatology has similarities with
Zoroastrianism.
[2] The text of the
Hebrew Bible was
redacted into its extant form in this period and possibly also
canonized as well.
Rabbinic Judaism developed during
Late Antiquity, during the 3rd to 6th centuries CE; the
Masoretic Text of the Hebrew Bible and the
Talmud were compiled in this period. "
Also as it mentions there they incorporated Persian Zoroastrianism in a big way.
A coming virgin born world savior was a Persian belief and Revelations and God at war with the devil were Persian myths first.
So that all makes sense and is how I would guess. Religous syncretism happens with every religion, Judaism is no exception. The information is from men writing stuff and sourcing other religions. Babylonain influence is the Mesopotamian stuff I think.
Revelations
the Persian Revelations that started this type of literature.
but Zoroaster taught that the blessed must wait for this culmination till Frashegird and the 'future body' (Pahlavi 'tan i pasen'), when the earth will give up the bones of the dead (Y 30.7). This general resurrection will be followed by the Last Judgment, which will divide all the righteous from the wicked, both those who have lived until that time and those who have been judged already. Then Airyaman, Yazata of friendship and healing, together with Atar, Fire, will melt all the metal in the mountains, and this will flow in a glowing river over the earth. All mankind must pass through this river, and, as it is said in a Pahlavi text, 'for him who is righteous it will seem like warm milk, and for him who is wicked, it will seem as if he is walking in the • flesh through molten metal' (GBd XXXIV. r 8-r 9). In this great apocalyptic vision Zoroaster perhaps fused, unconsciously, tales of volcanic eruptions and streams of burning lava with his own experience of Iranian ordeals by molten metal; and according to his stern original teaching, strict justice will prevail then, as at each individual j udgment on earth by a fiery ordeal. So at this last ordeal of all the wicked will suffer a second death, and will perish off the face of the earth. The Daevas and legions of darkness will already have been annihilated in a last great battle with the Yazatas; and the river of metal will flow down into hell, slaying Angra Mainyu and burning up the last vestige of wickedness in the universe.
Ahura Mazda and the six Amesha Spentas will then solemnize a lt, spiritual yasna, offering up the last sacrifice (after which death wW be no more), and making a preparation of the mystical 'white haoma', which will confer immortality on the resurrected bodies of all the blessed, who will partake of it. Thereafter men will beome like the Immortals themselves, of one thought, word and deed, unaging, free from sickness, without corruption, forever joyful in the kingdom of God upon earth. For it is in this familiar and beloved world, restored to its original perfection, that, according to Zoroaster, eternity will be passed in bliss, and not in a remote insubstantial Paradise. So the time of Separation is a renewal of the time of Creation, except that no return is prophesied to the original uniqueness of living things. Mountain and valley will give place once more to level plain; but whereas in the beginning there was one plant, one animal, one man, the rich variety and number that have since issued from these will remain forever. Similarly the many divinities who were brought into being by Ahura Mazda will continue to have their separate existences. There is no prophecy of their re-absorption into the Godhead. As a Pahlavi text puts it, after Frashegird 'Ohrmaid and the Amahraspands and all Yazads and men will be together. .. ; every place will resemble a garden in spring, in which
there are all kinds of trees and flowers ... and it will be entirely the creation of Ohrrnazd' (Pahl.Riv.Dd. XLVIII, 99, lOO, l07).