“He will be great.” Mary’s baby, the promised Messiah, “will be great.” This is an unqualified statement: Jesus will be great, period. In contrast, John the Baptist was foretold to be “great in the sight of the Lord [God]” (Luke 1:15). The Messiah would be great in every sense of the word, and would eventually rule the earth as king.
[For more on the coming kingdom of Christ on earth, see Appendix 3, “Christ’s Future Kingdom on Earth.”]
“will be called the Son of the Most High.” In the Bible, the Messiah was called the Son of God (although he was not the only one; cp. Ps. 2:7).