John Gill Commentary 2 Samuel 22:51

"Great deliverance giveth he to his king, And showeth lovingkindness to his anointed, To David and to his seed, for evermore." — 2 Samuel 22:51 (ASV)

[He is] the tower of salvation for his king: and shows
mercy to his anointed, unto David, and to his seed for evermore .
] (See Gill on Psalms 18:50).