What does Matthew 1:24 mean?

Based on what he knew at first, Joseph had every right—legally and morally—to divorce Mary (Matthew 1:18). The period of betrothal was treated as part of the marriage contract in this ancient time. Even though the couple had not yet lived together or had sex, they were legally bound together in virtually the same way as a fully married couple would be. Mary's pregnancy by another man would have given Joseph a legal and justifiable way to terminate his agreement. His initial plan was to do exactly that, but discreetly for Mary's sake (Matthew 1:19).

He did not follow through with that plan, however. God intervened by sending an angel to visit Joseph in a dream (Matthew 1:20–21). The angel revealed to Joseph what was really going on. Mary remained a virgin. The baby she carried came from the Holy Spirit. The boy would be called Jesus, from a Hebrew name meaning "Yahweh saves," and also Immanuel, meaning "God with us".

Joseph demonstrated remarkable faith in obeying God's command through the angel. He set aside the cost to his own reputation and defied cultural norms. Rather than taking the easy, socially simple path, he chose to obey God. Joseph ended the official betrothal period by taking Mary home to live with him immediately. This would have protected her and her family from scandal, as well as allowing him to provide for her throughout the rest of the pregnancy.

The following verse, though, makes it clear Joseph did not sleep with Mary until after the birth of Jesus. She remained a virgin, fulfilling the prophecy of Isaiah (Isaiah 7:14). After that time, Joseph and Mary would have other children together (Matthew 13:55–57; Mark 3:31–32).