Are we supposed to bow during these words of the Creed?
I used the small missal at Mass and noticed the instruction to bow during these words of the Creed: “by the power of the Holy Spirit he was born of the Virgin Mary, and became man." Is this a required posture?
Yes. According to the General Instruction of the Roman Missal, the faithful make a profound bow at the words of the Creed “by the power of the Holy Spirit he was born of the Virgin Mary, and became man":
The Creed is sung or recited by the priest together with the people with everyone standing. At the words et incarnatus est (“by the power of the Holy Spirit . . . became man") all make a profound bow, but on the Solemnities of the Annunciation and of the Nativity of the Lord, all genuflect. . . . A bow signifies reverence and honor shown to the persons themselves or to the signs that represent them. There are two kinds of bows: a bow of the head and a bow of the body.
- A bow of the head is made when the three Divine Persons are named together and at the names of Jesus, of the Blessed Virgin Mary, and of the saint in whose honor Mass is being celebrated.
A bow of the body, that is to say a profound bow, is made to the altar . . . in the Creed at the words Et incarnatus est . . . (GIRM 137, 275)