In the passage we see Thoreau seeking what he may believe to be unattainable. His sights are bound for something that will be "forever new and unprofaned." What he seeks is perfection.
The original wording in the lines before this is;
"There was a shepherd that did live,
And held his thoughts as high
As were the mounts whereon his flocks
Did hourly feed him by."
Thoreau's question is what happens when the flock seeks more than the shepherd........ thus, the shepherd would lose his flock. Today, the scientist, engineer, chemist, ect., are all seeking "higher meaning;" they seek more....... a computer programmer unwilling to take the next step will be left behind. All things created by man aren't possible without using their God given intelligence and a sense of imagination. Without using the talents we've been given there would be no advances in anything (medicine, technology, building).
It is laudable.............. not tragic