Three times, someone asks the speaker a question about their face: why it points upward, why it always wears a smile, why light always seems to fall on it. The speaker treats each question as a bit silly, something that only sets off giggles, makes a dying man smirk, or leaves darkness wondering. Then comes the same kind of reply each time, a gentle "Why, don't you know...?" that explains everything in one line.
The answers are happiness floats, smiles soar, and light makes one fly. Each stanza lifts a little higher, from floating to soaring to flying, just as the title promises. The speaker feels settled and joyful, almost amused that anyone would need this explained. The mood is playful and warm, with a quiet hopeful edge. The line about the dying man suggests that even someone near the end can be reached by a smile, and that cheerfulness here is a kind of answer to darkness rather than a way of ignoring it.