The Jewish custom of betrothal was a very joyful and solemn ceremony often officiated by a priest of the Temple.  The result was binding on the couple and their respective families, so much so that divorce was the only release possible - even before the actual wedding ceremony.

Again, nothing is said of St. Joseph in the New Testament prior to the Annunciation to Mary However, tradition has always described him as a builder and a carpenter from the town of Nazareth.  He is spoken of as a chaste, holy and just man -- a faithful Jew who would have compassion on his newly betrothed wife found to be with child before they were married. According to the Gospel of Matthew (Matthew 1.16), he was from the royal line of David.

The Gospel writers Matthew and Luke refer to the betrothal simply as a fact: In the sixth month, the angel Gabriel was sent to the town in Galilee called Nazareth, to a virgin betrothed to a man named Joseph of the House of David. (Matthew 1.18; Luke 1.26)

Mystics have often said that Mary and Joseph pledged to live a life of celibate chastity. The writers say that they were inspired by the Holy Spirit to surrender their love in preparation for the birth of Jesus the Christ, Son of the Most High.