In chapters 9-12 of Samuel, we learn how Saul was chosen by God to be the king of Israel and how he proved himself to the Israelites.
Samuel was told by God that Saul was the "goodliest" man in all of Israel and that he should be the king requested by the people. Saul first loses his father's donkeys and Saul and his servant got sent to find them. They asked where the "seer" was (a prophet) and they were sent to Samuel. Samuel was like, "Oh, snap! God told me yesterday that this guy would show up and that I should make him the king of Israel!" Samuel anointed Saul and told him not to worry about the donkeys, that they had been found. He also told him that he would run into prophets and would prophesy with them for a bit. This helped to establish to the people that Saul was a wise man. Then Samuel gathered Israel and announced that Saul would be their king (he was hiding out and they had to go find him). After announcing this, Saul wrote down in a book how the kingdom would be laid out.
In the wake of this announcement, some doubted Saul's kingly abilities. So, Saul took to the battlefield against the Ammonites and was victorious, proving his leadership abilities. He further proved his wisdom and justness by forgiving those who had doubted when it was suggested that they be put to death.
Now that Saul was solidly in place as the king, God had Samuel remind the people that God was the one responsible for all of their successes and deliverance from oppressors. And despite having a king, the people should never forget that God is the one behind the king who gives him power.
If anything we have read in the bible about the people of Israel so far could be any indication of what will happen, we can assume that the people will ignore this reminder from God and become full of themselves once again.....smite smite smite.....
As I'm writing this, I'm having a bit of an epiphany about the reason the people of Israel are chronicled in the bible. These stories are like looking into the mirror of our human existence. The Jews continuously forget about God every time things get good and God has to put them back in their place. This seems to be human nature. As soon as things start going well, we begin to forget the hard work (and help from God) it took to get to that point. Once we forget what got us there, we fail to work to maintain our momentum...and then we fall, only to have to start the cycle over again. These stories are the stories of how not to be. They are warnings of this cycle of mediocrity working to greatness only to fall to mediocrity again. Stand up and break the cycle. Remember what it took to get yourself on top and for once, work to stay there!