In Luke 1:46-49, Mary is praising her God, whom she considers aove all others. She begins by stating the her Lord is the lord of all creation and everyone and He deserves praise.
“My soul glorifies the Lord
47 and my spirit rejoices in God my Savior,
Then, in verses 50-55, Mary describes some of the great acts that He has performed, and she says that this proves how great he is. She tells of God destroying kings but lifting up the humble. She tells of Him feeding the hungry but sending away the rich.
Verse 55 reads:
"to Abraham and his descendants forever,
just as he promised our ancestors.”
Here, Mary is closing her praise song by reiterating His greatness and saying that He will continue to be wonderful forever, because they were promised this many years ago and he has continued to live up to this promise.