A speaker wakes up, or perhaps simply remembers, the night before: they cried over a child they have never met. The poem doesn't say whether the scream came from a dream, a real overheard moment, or something else, and that vagueness is part of what makes it unsettling. All we get is the child's desperate question, "Why do you do this to me!", which suggests someone being hurt by a person who should know better.
The main feeling is helplessness, as the title says. The speaker isn't angry or heroic, just stuck. The last line, "I could only listen," is flat and short, and it lands hard because listening feels like so little. The plain, simple wording adds to this. There's no decoration, as if the speaker is too shaken to dress the moment up. The mood is raw and sorrowful, with a quiet guilt underneath: caring deeply about someone you can't reach, and being unable to look away.