What does Matthew 1:18 mean?
Having concluded his genealogy of Jesus, Matthew begins telling the life of Jesus right from the beginning: Jesus' miraculous conception. Matthew does not spend nearly as much time introducing Mary as Luke's Gospel does. Instead, he focuses the story on Joseph and his response to the surprising news.Betrothal in Jewish culture was a binding agreement, often between the father of the bride and the husband to be. It was far more serious than the modern concept of engagement. If a woman slept with another man during the betrothal period, she was said to be guilty of adultery.
At first, Joseph didn't understand that Mary's pregnancy was the work of the Holy Spirit. He only knew that she was "found to be with child." This put him in the difficult place of deciding what to do about their upcoming wedding. The natural, common sense explanation for that situation is that Mary had been unfaithful. It's only when Joseph is informed by an angelic messenger that he realizes the full truth (Matthew 1:20).
Joseph's first response seems tempered by compassion. Rather than make a spectacle of Mary, his initial thought is to end the betrothal discreetly (Matthew 1:19).