He gained a world; he gave that world Its grandest lesson: "On! sail on!"

The couplet frames “gaining a world” not as conquest for its own sake but as the acquisition of a moral or imaginative horizon that can be handed on to others. The “grandest lesson” is rendered as an imperative—“On! sail on!”—which turns exploration into a metaphor for perseverance: keep moving forward despite uncertainty, risk, or opposition. In Miller’s characteristic celebratory mode, the figure praised is less a private hero than a public exemplar whose achievement becomes a shared cultural instruction. The line’s cadence and repetition of “world” emphasize both material discovery and the enlargement of human possibility.