The speaker describes a sudden, surprising return of old hopes, much like swallows that reverse their migration mid-sea at a trumpet call. These are hopes he thought he'd left behind, and they rush back with a force he can't quite comprehend. He's caught between the affectionate gaze of a woman and her words that pushed him away, between trusting his feelings or his logic. The warmth and confusion feel like a St. Martin's summer — an unexpected, fleeting warmth in the midst of autumn.
Even if the outcome disappoints him, he insists the dreaming itself was worthwhile. He's already harvested a "golden vision," something precious and real. The mood is bittersweet and reflective, never bitter. There's a quiet triumph in his tone: the sheer experience of hoping, however briefly, gives his life a sense of fullness. It's a gentle acceptance that some things are beautiful precisely because they don't last.