2 Samuel 22:51

He is the tower of salvation for his king: and sheweth mercy to his anointed, unto David, and to his seed for evermore.

He is the tower of salvation for his king. Here is a repetition of the figure used, 2 Samuel 22:3. "His king," the king whom He Himself chose and appointed.

And showeth mercy to his anointed. This phrase, being the special designation of the king of Israel, might be supposed limited in its application here to the author of the song; and therefore, in explanation of the comprehensive import of the term, he adds, "unto David, and to his seed for evermore," including all his royal posterity, and especially the Messiah, who is called David's seed (Acts 13:1; Romans 1:3; Galatians 3:16), his son (Psalms 89:27; Psalms 110:1, compared with Matthew 22:42), and the anointed king (Psalms 2:2). This song is a noble effusion of lyrical poetry. In the wide and discursive range of its survey all the salient points of David's life and experience are touched upon and described under a variety of bold and most striking images. As dedicated to a personal retrospect of the way by which David had been led, this song was a fitting hallelujah to be composed and sung at the close of his remarkable career. But, adapted also for public worship, it is a sublime, no less than a most appropriate, vehicle for the thanksgiving of devout worshippers; and containing as it does Messianic elements interspersed throughout, it has been, and will continue in future ages to be, one of the favourite songs of Zion.