David compares his time left to live on earth to a fading shadow. Alternate translation: "My time to remain alive is short like an evening shadow that will soon be gone" (See: [[rc://en/ta/man/translate/figs-simile]])
As David's body becomes weak and he is nearing the end of his life, he compares himself to withering grass. Alternate translation: "my body has become weak like withered grass" (See: [[rc://en/ta/man/translate/figs-simile]])