Four short lines carry a surprisingly dark thought. The speaker opens with a blunt complaint: nature treats us like "sacrificial brutes," as if we were animals led to slaughter for some larger purpose. Then the poem turns to a quiet image, the ground under an apple tree, waiting for fruit to fall. That picture can be read two ways. It may suggest that the earth, like nature in general, simply takes what comes to it, and that falling and decay are part of the cycle we're caught in. Or it may hint at a kind of patient waiting that has nothing to do with us at all.
The last line shifts the tone. "Still, the apple's sweet to me" is plain and almost shrugging. The speaker doesn't argue with the bleak view, but refuses to let it spoil a simple pleasure. The mood is wry and gently defiant: aware of life's harshness, yet content to enjoy the fruit while it lasts.