{And knew her not} (kai ouk egin(9373)ken aut(886e)). Note the
imperfect tense, continuous or linear action. Joseph lived in
continence with Mary till the birth of Jesus. Matthew does not
say that Mary bore no other children than Jesus. "Her firstborn"
is not genuine here, but is a part of the text in  Lu 2:7 . The
perpetual virginity of Mary is not taught here. Jesus had
brothers and sisters and the natural meaning is that they were
younger children of Joseph and Mary and not children of Joseph by
a previous marriage. So Joseph "called his name Jesus" as the
angel had directed and the child was born in wedlock. Joseph
showed that he was an upright man in a most difficult situation.