What does Luke 1:33 mean?

Jacob was the man renamed Israel by God (Genesis 35:10); his sons were the patriarchs of Israel's twelve tribes. Many Old Testament prophecies involve the Messiah, or the "Promised One," who would rescue Israel. This King would come from the tribe of Judah (Genesis 49:10) and the family line of David (2 Samuel 7:12–16). Those same prophecies indicated that once Messiah took the throne, He would never give it up (Isaiah 9:6–7).

The angel Gabriel is describing this Messiah to an unmarried virgin, Mary (Luke 1:26–27). The Savior he depicts will be born of Mary, herself (Luke 1:30–32). Most likely, Mary understood the angel's mention of David as a reference to Messiah. She would also have realized that calling Jesus "Son of the Most High" was a way of saying Jesus would be God incarnate (Hebrews 1:3; Luke 22:70; 2 Corinthians 1:19). Mary's praise of God later in this chapter demonstrates great familiarity with the Old Testament (Luke 1:46–56).

Jesus' birth will fulfill the associated prophecies. His sacrificial death and resurrection will make Him the Savior for all who come to Him in faith (John 3:16–17; 1 John 4:14). His return, in the end times, will be the moment He assumes His throne and ushers in an unending era of God's rule on earth (Revelation 19:11–16).