Whitman's, captain, my captain! What is the theme of?

Ah, captain, my captain used figurative rhetoric to compare the late President Lincoln to the captain and the victory of the Civil War to a ship about to dock, which was vivid and full of affection. In this paper, President Lincoln is compared to the captain who returned home full of victory and fell down when the ship was about to dock, expressing his infinite nostalgia and affection for President Lincoln.