The speaker is overflowing with happiness, so much that she wants to sing not just to people but to trees and stars. She has found love and feels loved in return — “he is mine” — and that certainty makes her feel complete. There is a striking paradox here: she says “Now at last I can die” and immediately “Now at last I can live.” The feeling is that this moment is so full and perfect that nothing else seems necessary, yet at the same time it makes her feel truly alive for the first time.
The imagery is light and unbounded: she is “sandaled with wind and with flame,” able to tread on grass or stars. The mood is wild, radiant, almost dizzy with joy. Everything feels possible.