What does the author mean when he refers to "men whose abilities have been made for a time useless by their passions or pleasures, and who having lost one part of life in idleness, are tempted to throw away the remainder in despair"?

The author means that men who throw away their opportunities, become mopey.

Explanation:

This is an excerpt from the life of swift, story by Samuel johnson.

In this excerpt, he talks about people who waste the opportunities given to them and realise it too late.

When they throw away the opportunities, don't use time wisely and spend their time in idleness, they are left with nothing.

They, then despair for the time spent unwisely and mope around feeling, that nothing can be achieved in the time left and lose all hope.

Samuel Johnson was an English writer who made contributions to English literature as a poet, biographer, moralist and a play writer.