He used all his endeavours to support Saul's house; which is mentioned, to show the reason of his deep resentment of the following aspersion. Or, he strengthened himself in the house of Saul, i.e. he so managed all affairs, as to get all the riches and power into his own hands; which made Ish-bosheth suspect that he aimed at the kingdom, and sought to marry the king's concubine in order to it, as the manner was. See 2 Samuel 12:8, 2 Samuel 16:21 1 Kings 1:17.
Related Commentaries of 2 Samuel 3:6
2 Samuel 3:6
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 for the house of Saul.