Théoden means to make this charge his last—one massive attack that will either win the battle or end in their deaths. Trapped in the fortress and faced with hopeless odds, Théoden seeks consolation against despair. While Legolas and Gimli use humor to fortify themselves, Théoden turns to action. He can’t bear to be idle with his thoughts and doesn’t have the same hope for the dawn that Aragorn still holds. And though he invokes the idea of song, it is this desire to take action, besides the obvious necessity of defeating Saruman’s armies, that leads him to make the charge, not any true hope of glory. It’s likely that, after the charge, there won’t be anyone left alive to tell the tale. Like Aragorn does when urging Legolas and Gimli to run swiftly after the hobbits during their hunt, Théoden speaks of a song as a sort of pledge to act in a way worthy of singing about.