Zacharias and Elizabeth were both getting old, too old to have kids. But Zach prayed, so an angel
appeared to tell him that God would take care of things for him. God would somehow get Liz pregnant and she'd have a son named John, who
would be filled with the Holy Ghost from the moment God, the angel, the Holy Ghost, or Zach (or maybe all of them working together) got
his mom pregnant. 1:7-15
Gabriel tells Mary that the Holy Ghost will come upon her and she'll be covered by the power of God,
so "the holy thing" that she delivers will be the Son of God. 1:35