The speaker is being hounded by a crow. It follows them home, fills their vision, and makes sure they are never truly alone. The bird is probably more than a bird. The poem suggests it stands in for something harder to name, such as anxiety, guilt, or a fear that tails the speaker everywhere. The crow's cries "ring through" them, and the line about tearing flesh makes the torment feel physical as well as mental.
The feeling builds from irritation ("mocks me") to helplessness ("I'm a mess") to outright terror in the last line, "I'm dying of fear." The short, plain lines and simple rhymes, like "home" and "alone," give the poem a nursery-rhyme beat, which makes it eerier. The repeated line "The crow it mocks me" works like a chant the speaker can't stop hearing. The mood is claustrophobic and dark, with no escape offered at the end.