"What They Died For" is an orchestral piece from the Season 6 soundtrack.
Jacob tells his final candidates that he brought them to The Island to replace him. He made the monster, ultimately causing his own death, and without a replacement, the monster threatens the whole world.
Sawyer challenges being used as a means to Jacob's ends, but Jacob explains that he chose flawed, lonely, hopeless people whom the Island could help. He explains that Kate stopped being a candidate when she became a mother but can still replace him if she wants. He then mentions the Light and says they must protect it and kill the Man in Black if they can.
The piece begins with the Island's history motif. It transitions into the home theme, which immediately gives way to the Light theme. It then moves into Jacob's theme. The piece ends on the main theme's counterpoint, followed by the main theme itself.
The title shares the episode's name. In the scene, Jacob explains to the remaining candidates why he brought them to the Island, and therefore the purpose the other candidates were sacrificed for.