Chat-GPT (Apr 17th 2023): The sentence by George MacDonald is describing how people experience emotions.
The first part of the sentence, "When a feeling was there, they felt as if it would never go," means that when someone is experiencing a certain emotion, it can feel very intense and overwhelming, as if it will never go away.
The second part of the sentence, "when it was gone, they felt as if it had never been," means that once the emotion passes, it can feel like it never happened or like it wasn't that important.
The third part of the sentence, "when it returned, they felt as if it had never gone," means that if the same emotion comes back, it can feel just as intense and overwhelming as the first time, even if it had previously passed.
Overall, the sentence is highlighting the intense and ever-changing nature of emotions, and how they can feel all-consuming when present and nonexistent when gone.