I am still reading through 1 and 2 Samuel for my own devotional time and I am starting to pick up on a theme. God's kingdom and God's plan cannot be grasped at or achieved by us on our own initiative. It is gifted to us by God in God's timing.
David is promised to be the new king after Saul loses favor with God...but notice David's resolve. Two times in 1 Samuel 24-26 he has the opportunity to kill Saul and speed up the process. And it seems reasonable that he has a right to do this because Saul has tried to kill him numerous times...but David stands down...resists the grasp and waits for the gift.
Then when Saul dies, an Amalekite brings David news of this, thinking there would be great rejoicing at the news...Instead, David has the Amalekite killed and then grieves passionately at the loss of Israel's king.
With Saul out of the picture, David is still not the next in succession. Saul has a son remaining, Ish-Bosheth (also known as Ish-Baal). Ish's general, Abner defects to David's side, but is killed by David's general, Joab. Abner had quite a following and his death both benefited and hindered David's likelihood of succession to the throne. David, showing that he was not about to take the throne by his own conniving, manipulation, coersion, cursed Joab and his own military at Abner's death.
Then Ish-Bosheth, weakened and fearful after Abner's departure is killed during a nap by two of his own military leaders. The leaders bring his head to David seeking approval, but David has the men killed for their bloodguilt.
Integrity and obedience are the keys to the Kingdom. David waited for the gift to be given, rather than to go apprehend the gift. There will come a time where David will try to seize what he wants (Bathsheba) and there will be terrible consequences for this...but the first few chapters of 2 Samuel suggest that David was innocent of all the political games and treachery that often come with leading a kingdom.
As we participate in the Kingdom of God being established in the world, we must remember that it is not taken by force or might. But it is a gift that we receive as the people of God through our witness to the King and our obedience and allegiance to Him.