A.T. Robertson Commentary Matthew 1:25

"and knew her not till she had brought forth a son: and he called his name JESUS." — Matthew 1:25 (ASV)

And knew her not (κα ουκ εγινωσκεν αυτην). 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.