Four short lines, and the whole poem is a quick portrait of a bird. The speaker praises the wren above all for its curiosity, calling it "most excellent," and that simple, admiring tone sets the feeling: affection, a little amusement, and real respect for something so small.
The best touch is the idea of the wren as "a scholar of the afternoon hill." A scholar studies things closely, and that is exactly how a wren behaves when it hops and pokes about, investigating everything in reach. The last line, "supping and discoursing," makes the bird sound like a person at a dinner table, eating while chatting about big ideas. Judging by the wording, the speaker may be hearing the wren's song as conversation. The mood is light, warm, and unhurried, like a lazy afternoon spent watching a bird and enjoying how busy and sociable it seems.