The speaker sits in a field and feels welcomed by it. The land "receives" them, almost like a host, yet the speaker admits they understand only a small part of the world. That part is boiled down to a few quiet images: "a well an idle heart." With no punctuation, the well and the idle heart sit side by side, as if they were the same thing, something deep that is waiting to be used or filled.
The last lines turn toward solitude. The speaker has been alone "here at the present / infinite spot," and the phrase squeezes something huge into something small. A single place, right now, becomes endless. The mood is calm, humble and a little wistful. There is no drama, only stillness and the sense that not understanding much is fine when you are paying close attention to where you are. Loneliness here feels less like a lack and more like room to breathe.