2 Samuel 3:9

So do God to Abner, and more also, except, as the LORD hath sworn to David, even so I do to him;

The verse is Abner's oath to do for David what the Lord had sworn to him. He had long stood against David even though God had appointed David, hoping to secure honor for himself. Incensed against the weak and incompetent Ishbosheth, and moved by resentment, wounded pride, and passion, he abandoned Saul's cause.

He deserted to David and offered to bring all the tribes of Israel over to him. David accepted the offer and sent Abner away with honor to carry out his purpose. In this Abner hoped to gain for himself the highest place in David's service. Yet his ambition and influence, joined with his lack of godliness, could have endangered David's throne and the peace of the nation.