In William Holman Hunt's Own Words:

Shakespeare's song represents a Shepherd who is neglecting his real duty of guarding the sheep: instead of using his voice in truthfully performing his duty, he is using his "minikin mouth" in some idle way. He was a type thus of other muddle headed pastors who instead of performing their services to their flock — which is in constant peril — discuss vain questions of no value to any human soul. My fool has found a death's head moth, and this fills his little mind with forebodings of evil and he takes it to an equally sage counsellor for her opinion. She scorns his anxiety from ignorance rather than profundity, but only the more distracts his faithfulness: while she feeds her lamb with sour apples his sheep have burst bounds and got into the corn. It is not merely that the wheat will be spoilt, but in eating it the sheep are doomed to destruction from becoming what farmers call "blown."

—Victorian Web