Albert Barnes Commentary Luke 1:51

"He hath showed strength with his arm; He hath scattered the proud in the imagination of their heart." — Luke 1:51 (ASV)

Hath showed strength with his arm (Luke 1:51). The arm is the symbol of strength. The expression in this and the subsequent verses has no particular reference to his mercy to Mary. From a contemplation of his goodness to her, she enlarges her views to a contemplation of his goodness and power in general, and to a celebration of the praises of God for all that he has done to all people. This is the nature of true piety. It does not terminate in thinking of God's mercy toward ourselves. It thinks of others, and praises God that others also are made partakers of his mercy, and that his goodness is manifested to all his works.

He scattereth the proud (1 Samuel 2:9; Daniel 4:37). he has often done it in time of battle and war. When the proud Assyrian, Egyptian, or Babylonian had come against the people of God, he had often scattered them and driven away their armies.

In the imagination of their hearts. Those who were lifted up or exalted in their own view. Those who thought themselves to be superior to other people.