Mary used this polite expression to say that she had not engaged in sexual activity. AT: "I am a virgin." (See: [[rc://en/ta/man/translate/figs-euphemism]])
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.
# So the holy one to be born will be called the Son of God
This can be stated in active form. AT: "So they will call the holy one who will be born 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]])