‘And Joseph arose from his sleep, and did as the angel of the Lord commanded him, and took to himself his wife, and knew her not until she had brought forth a son, and he called his name JESUS.'
Note how it is made clear that this was a genuine dream. There is no suggestion that the angel had actually been present, except in his thoughts. Thus far from so-called ‘legendary accretions' the opposite is the truth. On the other hand Joseph had no doubt that a messenger from the Lord had spoken to him, and the result was that he altered his plans and invited Mary to be wedded to him and come to live with him. ‘He took to himself his wife'. But what he did not do was ‘know' her, that is, have sexual relations with her. And he did not do so ‘until she had brought forth a son'. The Greek construction used here clearly indicates that after that he did so. Had there been any truth in the idea of her perpetual virginity this would have been the point at which it would have been emphasised.
‘Called His name Jesus.' Joseph's naming of Jesus was important. It was his final act by which he acknowledged Him as his son. From then on no one could deny it. Compare Isaiah 43:1, ‘I have called you by name, you are Mine'. Jesus was now the acknowledged heir to the throne of David. Passing on the heirdom through an adopted son was perfectly acceptable.