Final answer:
The feast that celebrates Jesus' conception is called the Annunciation. It marks the moment when the archangel Gabriel announced to Mary that she would conceive the Son of God through the Holy Spirit.
Step-by-step explanation:
The feast that celebrates Jesus' conception is called the Annunciation. It is commemorated on March 25 and is based on the biblical account from Luke 1:26-38.
The Annunciation marks the moment when the archangel Gabriel announced to Mary that she would conceive the Son of God through the Holy Spirit. This event is significant as it signifies the beginning of Jesus' earthly existence and Mary's willingness to be the mother of the Messiah.