As the poem opens, the speaker is rambling in the moors on a beautiful, sunny day, but instead of giving him joy, as it usually does, the natural world leaves him full of "dejection." He is fearful and sad, thinking of the future and worrying that he might someday he might age and face:
Solitude, pain of heart, distress, and poverty.
At this point he sees the leech gatherer. He describes him as very old:
the oldest man he seemed that ever wore grey hairs.
He is so old that he is bent over so that his head and feet seem to come together. He looks like he might be doubled over with either physical sickness or a deep emotional pain. He leans on a long gray staff to support his weight. He is still for a long time, then he stirs the pond with his staff. This movement inspires the speaker to talk to him.
The speaker describes the leech gatherer's speech as "feeble," but notes that his eyes still are "vivid." His voice has a "lofty" and "stately" sound that impresses the speaker. He sounds "grave" and "religious." His words seem to carry weight.
As they talk, the speaker learns the the old man goes from pond to pond gathering leeches to sell. (At that time leeches were used for medicinal purposes.) The leech supply has dwindled, and the old man is very poor, but he nevertheless earns enough to stay alive. The speaker describes his character as "cheerful" and "kind," and his mind as "firm." By the end of the conversation the speaker feels renewed: the old man's cheerful character despite his poverty and adversity has made the speaker feel "I could have laughed myself to scorn" for being so sad and worried about the future earlier. The leech-gatherer is an example of how to live with grace and dignity despite old age and poverty.