the birth of Jesus Christ was on this wise: When as his mother Mary was espoused to Joseph

Matthew 1:18 ¶ Now the birth of Jesus Christ was on this wise: When as his mother Mary was espoused to Joseph, before they came together, she was found with child of the Holy Ghost. ¹⁹ Then Joseph her husband, being a just man, and not willing to make her a publick example, was minded to put her away privily. ²⁰ But while he thought on these things, behold, the angel of the Lord appeared unto him in a dream, saying, Joseph, thou son of David, fear not to take unto thee Mary thy wife: for that which is conceived in her is of the Holy Ghost. ²¹ And she shall bring forth a son, and thou shalt call his name Jesus: for he shall save his people from their sins.

The Feast of the Annunciation is one of the twelve Great Feasts of the church year. As the action initiating the Incarnation of Christ, Annunciation has such an important place in Eastern theology that the Festal Divine Liturgy of St. John Chrysostom is always celebrated on March 25, regardless of what day it falls on—even if it falls on Pascha (Easter Sunday) itself, a coincidence which is called Kyriopascha. The only time the Divine Liturgy may be celebrated on Great and Holy Friday is if it falls on March 25. Due to this, the rubrics regarding the celebration of the feast are the most complicated of all in Eastern liturgics. The Annunciation is called Euangelismos (Evangelism) in Greek, literally meaning "spreading the Good News".

St. Ephraim the Syrian taught that the date of the conception of Jesus Christ fell on 10 Nisan on the Hebrew Calendar, the day in which the passover lamb was selected according to Exodus 12. Some years 10 Nisan falls on March 25, which is the traditional date for the Feast of the Annunciation and is an official holiday in Lebanon.