The title here is Aged Ignorance and what Digby called the couplet(?) was " In Aged Ignorance profound,
Holy and cold, I clipp'd the wings
Of all sublunary things,":
Digby says on page 43): "This refers to the tendency to try to explain everything in life by the known." How about the man in the middle of the 19th century who lamented because he felt that everything possible had already been invented.
Wieman referred to it as the created good, at the expense of the creative event. There are many ways to express this fundamental truth of the human psyche; one of them is conservative vs liberal (generic, not necessarily political).
With those three lines and small image Blake can make us aware of this fundamental truth of the human psyche. We live in Plato's Cave, with "chains of the mind locked up", unable to move away from our prejudices, and only when we become aware of our deplorable condition do we have a chance to turn and look for the light. As AA can tell you, you have to hit bottom first.
In an earlier post (called Clipped) the matter was discussed in terms of the generation gap; some kids leave home at the earliest opportunity, and there may be good reasons for that decision.