The speaker begins in a low place. He admits that he often feels weak and useless, and that life has seemed so dull he has wished death would simply dissolve it, like acid eating through metal. That image is cold and harsh, and it sets a bleak tone.
Then the poem turns on the word "Yet." He lists what he hasn't forgotten: sunlit water, a woman's voice, dancers, worshippers, a crying child, wind in the hills. The lines get short and quick, almost like flashes of memory, and the mix of joy, devotion and sorrow suggests he values all kinds of human and natural experience, not just the pleasant ones.
The ending makes his claim plain. These memories, he says, are "more of me" than his wrinkled face or aching heart. His body and his sadness are real, but they don't define him. The mood moves from exhaustion to a quiet, hard-won consolation.