The process of Mary's conception would begin with the Holy Spirit coming to her.
# will come upon
"will overtake"
# the power of the Most High
It was God's "power" that would supernaturally cause Mary to become pregnant even while she still remained a virgin. Make sure this does not imply any physical or sexual union—this was a miracle.
# will come over you
"will cover you like a shadow"
# So the holy one to be born will be called the Son of God
This can be stated in active form. Alternate translation: "So the holy one who will be born they will call the Son of God" or "So the baby that will be born will be holy, and people will call him the Son of God" (See: [[rc://en/ta/man/translate/figs-activepassive]])