“But while he thought on these things, behold the angel of the Lord appeared to him in his sleep, saying: Joseph, son of David, fear not to take unto thee Mary thy wife, for that which is conceived in her, is of the Holy Ghost.” (Matthew 1:20)
Literal Sense: Mary was found to be with child and the angel of the Lord appeared to Joseph to assure him that she was not unfaithful but that the child within her womb was conceived by the Holy Spirit.
Allegorical Sense: Just as the Holy Spirit used Mary’s body to create the body of Christ, the Holy Spirit uses the elements of bread and wine, and after changing the substances of the elements, He makes present the body, blood, soul and divinity of Christ.
Moral Sense: As the Holy Spirit formed the body of Christ within Mary’s body, the Holy Spirit forms Christ within our bodies (Galatians 4:19). Since Christ lives within us, we must constantly strive to treat our bodies as holy.
Analogical Sense: God took on human flesh through the Virgin Mary in order that human flesh might be united and elevated to divinity: “[f]or the Son of God became man so that we might become God.” (Catechism of the Catholic Church, Paragraph 460, quotation from St. Athanasius, De inc. 54, 3: PG 25, 192B)