What does Luke 1:54 mean?

These words are part of Mary's song of praise, sometimes called "The Magnificat." This began (Luke 1:46) in reply to her relative, Elizabeth, who was celebrating Mary's role in bearing Jesus Christ (Luke 1:39–42). While acknowledging her need for a Savior (Luke 1:47), Mary has also made many references to the Old Testament. Some are in the form of quotations. Others are echoes of biblical ideas. These not only praise God for what He has done (Luke 1:51; Psalm 89:13), and who He is (Luke 1:49; Psalm 50:1; Exodus 15:11), they also celebrate how the Messiah will accomplish these things on an eternal scale (Luke 1:52–53; Revelation 21:1–5).

Prophecies about a Promised One were centered around the nation of Israel. This Messiah was to come from the tribe of Judah (Genesis 49:10) and the family line of David (2 Samuel 7:12–16). He would fully accomplish the promises made to Jewish ancestors such as Abraham, Isaac, and Jacob (Isaiah 9:6–7). Isaiah records God referring to Israel as His servant and promising not to forsake the nation (Isaiah 44:21). This once again demonstrates the mercy God shows (Psalm 25:6; 86:15) to those who trust and honor Him (Deuteronomy 5:10; Psalm 103:17).