Steve listens to the composition that he and his daughter created together and is at peace. He compares life to a song and finally feels God's presence in the world.
Steve's last chapter is the realization of what he has been searching for: the nature of God, who is "love in its purest form." Everything that Steve had longed for, he already had — time with his music, his son, and his daughter.
As important as it is for Ronnie to play, it is also important for Steve to listen, so that they shared something together. Steve created the stained-glass window with his son and a musical composition with his daughter. Both are tangible things that will serve as a reminder of their time together.
Initially, it seems very obvious that Ronnie is the protagonist of The Last Song; yet, some of the most important ideas about God and love and parenting are experienced and learned by Steve. Would it be fair to consider him a co-protagonist, especially because of the number of important chapters told from his point of view?
Steve is, without question, intrinsic to the story. It's hard to write a quality father-daughter story if the reader doesn't understand — and sympathize with — the father. In addition, Steve's character provides the drama and tragedy in the story. The reader needed to care about him.