It seems clear that Abner recognized the fact that the Lord had promised the throne of Israel to David.1 He must have known this when he supported Ish-bosheth after the death of Saul.2 After all, he was present with Saul when Saul publicly told David that he knows that David will be king after him (1 Samuel 24:20).
9 God do so to Abner and more also, if I do not accomplish for David what the LORD has sworn to him,