When the early Christian Jews concluded that the appearances of the YHWH Angel prior to Jesus' birth must also have been Jesus somehow, this gave Jesus a pre-existence and it shifted the paradigm. No longer was he a normal human being born of normal human parents. Somehow this great Angel had been embodied either at Jesus' conception or his quickening. In other words, a human fetus was possessed by this Angel, rather than a human man at his baptism. The Christians shifted his possession to the earliest moment possible. The idea that an angel can possess a human being is possible because the ancient people understood "spirits" and "angels" to be equivalents. This is also the case with the word "powers." The angel was a spirit who like a demon could possess a human being.
The virgin birth stories are related to this shift. The story of womb-possession is very prominent in Luke's gospel, which parallels John the Baptist's conception with Jesus'. John the Baptist was "filled with the Holy Spirit even from his mother's womb" (Luke 1:15). Jesus' conception is understood similarly, as the Holy Spirit, the Power of the Most High, coming upon Mary so that her child would be the holy Son of God. Keep in mind that angels are sons of God. And prophets are called and consecrated (which means a descent of the Holy Spirit into them!) from before they came into the womb of their mothers (see Jer 1:5; Isa 49:1; cf. Gal 1:15).
In Matthew, the relationship of Jesus to the Holy Spirit is framed in terms of agency. Mary is found "having [a fetus] in her womb FROM the Holy Spirit" (1:18). This is another shift in this christological pattern. It moves the concept of a divine fetus to divine parentage rather than spirit possession. This shift may have been popular with Hellenistic audiences familiar with stories of gods siring heroes.
I think it is significant that since these two authors think that the embodiment of the Spirit happened to the fetus in the womb, both Matthew and Luke independently shift the Markan baptism account of possession of the Spirit "in" Jesus (eis: Mark 1:10) to "upon" him (epi: Matt 3:16; Luke 3:22). Since he has had the Spirit in him since the womb, the baptism is reconceived as an outward anointing of the Spirit.
Next post we will look at Justin Martyr who preserves this paradigm in its entirety.