The book of 1 Samuel focuses on three characters: Samuel, Saul, and David. A poem near the start of the book reveals the book's key themes: God’s opposition to the proud, exultation of the humble, faithfulness in spite of evil, and the promise of a messianic King.
These themes are played out through the rest of the book as we see Saul rise to power, only to have his character flaws exposed as he disobeys God’s command. In contrast, God raises up David, a humble shepherd who trusts God. As the story progresses, we see these two characters in increasingly stark contrast. Saul slips into madness as David resolutely trusts in God’s timing and purposes.