If we were not so single-minded …

A. Poet is saying to Human beings. "We’ refers to the human beings, who are always thinking about their own progress and advancement.

C. People pursue single-mindedly on keeping their lives moving. ..The poet suggests that it would be better if they give themselves rest for sometime. For once they may do nothing.

D. The poet urges them to stop for a while and take some moment to relish on what they have achieved till now. Everyone here is living a life in which he wants to achieve various things one after another. But now the poet says it is the time to stop and see what has been achieved and should be enjoyed. This will help us skip the sadness which has become so prominent in our lives. The sadness of not enjoying what we have achieved and the greed to achieve what next is in the list to be achieved.