The angel answered her, "The Holy Spirit will come on you, and the power of the Most High will overshadow you. Therefore also the holy one who is born from you will be called the Son of God.
In the book of Revelation, again, that glorious song that Handel has put to music, "King of Kings and Lord of Lords, forever and ever, hallelujah, hallelujah."So the angel is telling about the eternal reign of Jesus Christ.