When Gabriel tells Mary that she is going to have a child, her mind must have heard the echos of Abraham and Issac, but mostly Samson.  Just like Jesus, Samson's birth was announced to a common and unsuspecting mother by an angel.  And just like Samson, Jesus would be a deliverer of his people.  What's more, he would have the name Jesus - literally Joshua.  He would lead his people to finally possess the land/blessing God had promised.