2 Samuel 3:18
Now then do it: for the LORD hath spoken of David, saying, By the hand of my servant David I will save my people Israel out of the hand of the Philistines, and out of the hand of all their enemies. Now then do it: for the LORD hath spoken of David, saying, By the hand of my servant David I will save my people Israel out of the hand of the Philistines, and out of the hand of all their enemies.
Abner broke with Ishbosheth, whose throne had been set up by malice and ambition despite his weakness and incompetence, to offer to bring over all the tribes of Israel to David. This appeal invoked the Lord's declared purpose to save Israel from the Philistines and from all their enemies by the hand of His servant David. David accepted Abner's proposals and sent him away honorably to carry out the transfer of the kingdom.
The warm reception given to so valiant and famed a warrior stirred the jealousy of Joab, the commander of David's army. Joab also bore a blood-feud against Abner because Abner had killed his brother Asahel in the war between Israel and Judah. Seizing the moment, Joab waylaid and murdered Abner both to avenge his brother and to remove a prospective rival.