Today’s Question on BustedHalo is answered by moi.

What part did Mary’s biology play in the making of the person of Jesus Christ?

Mike Hayes Anwsers:
The mission of the Holy Spirit is always conjoined and ordered to that of the Son. The Holy Spirit, “the Lord, the giver of Life”, is sent to sanctify the womb of the Virgin Mary and divinely fecundate it, causing her to conceive the eternal Son of the Father in a humanity drawn from her own.” (CCC, 485)
The word “fecundate” means to impregnate. So the best explanation we have lies here that is was the power of the Holy Spirit that makes her pregnant.
That implanting of a divine nature with Mary’s female human egg that starts Mary on the cycle of pregnancy.
I hesitate to say that it was “divine sperm cells” that unite with the egg because that is how we might understand this scientifically in our human experience and indeed this may be how the Holy Spirit was able to impregnate Mary–but we don’t really know that for certain.
This is a miracle, something that confounds science and even goes beyond it into something of a mystery.

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