The speaker says they have nothing to give except words, and the poem spends most of its length showing how fragile those words are. Image after image carries them off: birds flying away, speech lost to the wind, a river that flows on forever, the sea, a thinning mist. Nothing here stays put. Even the line about a kiss suggests that a memory can fade as easily as a sound.
The mood is wistful and a little sad, but it isn't bitter. The speaker seems humble, almost apologetic about having so little to offer. Then the last line turns warm and generous: "if you want them, they're yours." The words may not last, but they are all the speaker has, and they are given freely. The repeated opening line, "All I have is words," makes that closing offer feel sincere and quietly moving, a small gift handed over with open hands.