"Abner conferred with the elders of Israel and said, "For some time you have wanted to make David your king. Now do it! For the LORD promised David, 'By my servant David I will rescue my people Israel from the hand of the Philistines and from the hand of all their enemies.' " (2 Samuel 3:17, 18)
Abner, here, is reminding the elders of Israel what God had promised David. David was to be king over all the land and he was going to rescue the Israelites from their enemies. David had been anointed king over the house of Judah, but not as king of all Israel. Things had not progressed as David would have desired but God was at work. Abner, who was on Saul's side defected to David's side because of an argument with Saul's son Ishbosheth. Thus started a process by which David would be king. Abner was murdered by Joab, because Abner had killed his brother Asahel. Ishbosheth was murdered later on by Baanah and Recab, leaders of his raiding bands.
Then the Bible says,
All the tribes of Israel came to David at Hebron and said, "We are your own flesh and blood. In the past, while Saul was king over us, you were the one who led Israel on their military campaigns. And the LORD said to you, 'You will shepherd my people Israel, and you will become their ruler.' " When all the elders of Israel had come to King David at Hebron, the king made a compact with them at Hebron before the LORD, and they anointed David king over Israel. David was thirty years old when he became king, and he reigned forty years. In Hebron he reigned over Judah seven years and six months, and in Jerusalem he reigned over all Israel and Judah thirty-three years. (2 Samuel 5:1-5)
God's promises to David that he would be king over all Israel were fulfilled, not partly, but fully, in God's time.
His promises to you regarding any matter will also be fulfilled totally in his wonderful time. Keep praying.