What does Luke 1:50 mean?

Elizabeth reacted to the presence of Mary's unborn child (Luke 1:31–33) with Spirit-driven praise, as did her own unborn son (Luke 1:39–42). Mary, in turn, is responding with an extended song of praise (Luke 1:46). This draws from many parts of the Old Testament, whether by quoting verses or referencing broad ideas. Mary has already worshipped God as her Savior (Luke 1:47) and alluded to God's blessing of Hannah, the mother of the prophet Samuel (Luke 1:48; 1 Samuel 1:11; 2:1).

The prior verse noted God's great power (Luke 1:49; Psalm 50:1; 62:7; 106:2) as well as His holy perfection (Exodus 15:11; Leviticus 20:26; Psalm 99:5). The words of this verse resonate with that by declaring this holy, almighty God is also merciful (Psalm 25:6; 86:15), for generation after generation who honor Him. The "fear" she speaks of here is in the typical biblical sense of reverence and awe; this is humble submission, not abject terror.

Her words are probably a paraphrase of Psalm 103:17, as well as an agreement with Deuteronomy 5:10.