15 When at the Annunciation Mary hears of the Son whose Mother she is to become and to whom "she will give the name Jesus" (= Savior), she also learns that "the Lord God will give to him the throne of his father David," and that "he will reign over the house of Jacob for ever and of his kingdom there will be no end" (Lk. 1:32- 33). The hope of the whole of Israel was directed towards this. The promised Messiah is to be "great," and the heavenly messenger also announces that "he will be great"-great both by bearing the name of Son of the Most High and by the fact that he is to assume the inheritance of David. He is therefore to be a king, he is to reign "over the house of Jacob." Mary had grown up in the midst of these expectations of her people: could she guess, at the moment of the Annunciation, the vital significance of the angel's words? And how is one to understand that "kingdom" which "will have no end"? Although through faith she may have perceived in that instant the was the mother of the "Messiah King," nevertheless she replied: "Behold, I am the handmaid of the Lord; let it be to me according to your word" (Lk. 1:38). From the first moment Mary professed above all the "obedience of faith," abandoning herself to the meaning which was given to the words of the Annunciation by him from whom they proceeded: God himself.
Source: Redemptoris Mater (Vatican.va)