A Jew Speaking to Jews

All this took place to fulfil what the lord had said through the prophet. When joseph woke up, he did what the angel of the lord had commanded him and took mary home as his wife. But he did not consummate their marriage until she gave birth to a son, and he gave him the name jesus. And you read a line thereabout a fulfilled prophecy. Can you go back to the emmanuel portion? That is a weird reference. We take that for granted as we read, cause we want that prophecy to be about JESUS. So why is matthew calling this to mind? I think matthew is calling that to mind to say those days