Albert Barnes Commentary 1 Samuel 26:15

"And David said to Abner, Art not thou a [valiant] man? and who is like to thee in Israel? wherefore then hast thou not kept watch over thy lord the king? for there came one of the people in to destroy the king thy lord." — 1 Samuel 26:15 (ASV)

This incidental testimony to Abner’s great eminence as a warrior is fully confirmed by David’s dirge at Abner’s death (2 Samuel 3:31–34, 38), as well as by his entire history. At the same time, David’s bantering tone toward Abner, coupled with what he says in 1 Samuel 26:19, makes it probable that David attributed Saul’s persecution of him in some degree to Abner. Abner would be likely to dread a rival in the young conqueror of Judah (compare to 2 Samuel 2:8).