The speaker begins with a flat admission: truth is something they can't have. Next to that, melancholy is pictured as a desert, a wide, dry, empty place. Yet the tone stays quiet and unshowy. They go to work, and it's "well enough," a phrase that sounds neither happy nor miserable, just getting by.
The middle stanza pushes away big ambitions. The speaker doesn't want to write a book, or even "live in one," which suggests a wish to avoid turning life into a polished story or a grand piece of meaning. Then comes the turn: "but I must confess." The word "confess" makes singing sound almost like a secret, something slightly embarrassing. Out in the fields, away from work and from the pressure to say something true, the speaker simply sings. The mood is subdued and wistful, but it ends with a small, warm release. Song, rather than truth, seems to be what makes the desert bearable.