Charles Ellicott Commentary 2 Samuel 3:6

"And it came to pass, while there was war between the house of Saul and the house of David, that Abner made himself strong in the house of Saul." — 2 Samuel 3:6 (ASV)

Abner made himself strong. —It has already been noticed that the fortunes of the house of Saul depended entirely upon Abner, but the fact of Ish-bosheth’s great obligation to him is again mentioned here in explanation of the following story.