Enotes has an excellent discussion of this beautiful collection of essays by Dillard.  All of her meditations on nature arise from her observation of it:  she doesn't interfere with it (generally) but finds it interesting and respects it as an entity that deserves to live its course.  One excerpt from enotes says: "The narrator is determined to present the natural world as it truly is, not sentimentally or selectively. Therefore, she is as likely to reflect on a frog being sucked dry by an insect as on the slant of light that strikes a certain springtime tree. Whether the images are cruel or lovely, the language is beautiful and poetic, and insistently celebratory."  And the language signifies the place of humans in relation to nature.