Virgin Birth (origin)
A depiction of Isis, in the form of a kite or falcon, on the walls of Dendera Temple (37AD), getting pregnant with the sperm of the deceased but resurrected-for-a-moment god Osiris, which became, during the Roman recension, the story of Mary getting pregnant via the powers of the Holy Spirit; a monotheistic retelling of a polytheistic story, in short.
In religio-mythology, Holy Spirit is a monotheistic rescript of mythical lightening-flash, time-stopped, powered sperm of the dead but resurrected-for-a-moment god Osiris.

Overview
In In c.2000BC, in Spell 148 of the Coffin Texts, what would eventually become, in the Roman recension, the "Holy Spirit" that impregnates the Virgin Mary, is described according to a story wherein the goddess Isis, after dreaming about turning into a falcon, or something to this effect, wakes up pregnant with the seed of the deceased god Osiris: [1]

Isis, taking the shape as a Falcon. The lightening-flash strikes [see: black rite] and the gods are afraid. Isis wakes pregnant [see: virgin birth] with the seed of her [deceased] brother [husband] Osiris. She is uplifted, even she the widow [of the dead Osiris], and her heart are glad with the seed of her brother Osiris. She says: ‘Oh gods! I am Isis the sister of Osiris who wept for the father of the gods, Osiris, who settled the slaughterings of the Two Lands [Upper Nile/Lower Nile]. His seed is within my body, and it is as the son of the foremost of the Ennead who will rule this land and who will become heir to Geb [Joseph] and who will speak for his father and who will slays Seth, the enemy of his father Osiris, that I have molded the shape of the god [Horus] within (my) egg. Come, Oh gods, so that you shall make his protection within my womb. Know in your hearts that your lord is he, this god, who is in his egg, blue(?) of form, the lord of the gods. Great is their beauty, namely (that of) the blue barbs(?) of the two plumes’.”

In short, during the Roman recension (100-500AD), the above polytheism of gods, specifically: Isis, Osiris, Set, Horus, Geb, Ennead, are converted, via the god-to-prophet technique of the Hebrews, into a newly reformulated monotheism, wherein the “seed of her [deceased] brother [husband] Osiris”, intermixed with the resurrection powers of “lightening flash strikes”, during which the god Thoth makes time stop (see: black rite), becomes the “Holy Spirit”, Isis becomes the Mary, Geb becomes Joseph, Set becomes Satan (or the devil), and Horus becomes Jesus.

References
1. (a) Faulkner, Raymond. (1968). “Translation of Spell 148 of the Coffin Texts”, The Journal of Egyptian Archeology, 54:40-44.
(b) Gilula, Mordechai. (1971). “Coffin Texts Spell 148” (ΡΊ), The Journal of Egyptian Archaeology, 57:14-19, Aug.
(c) Luckhert, Karl. (1991). Egyptian Light and Hebrew Fire: Theological and Philosophical Roots of Christendom in Evolutionary Perspective (pg. 92). SUNY Press.

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