Through the example of David's life after Saul, the book of 2 Samuel reveals the successes and failures that any individual experiences, including kings.
After the death of Saul, David unifies the twelve tribes as their king. In his new capital of Jerusalem, David desires to build God a house. Instead, God promises to build David an eternal house through a king from his lineage. This is a key moment in the book of 2 Samuel and in the Hebrew Scriptures that point us toward a messianic king who will come to fulfill the promise given to David and Abraham to bless all nations.
However, we soon discover that David is not that king. After failing spectacularly, the kingdom slowly unravels. The final chapters of 2 Samuel highlight moments of David’s weakness, showing us his own failure as similar to Saul’s, while promising another king who will come to fulfill God’s good purposes.