meaning of the words underlined

Sanjay, perhaps you are asking about the meaning of "splitting hairs"? 

Splitting hairs is a metaphor. Let's think about the phrase literally.  How would you split a hair?  With a very sharp knife, a microscope (to see the hair), and something to hold the hair (so it won't wiggle) when we try to split it.  In other words, it is a very difficult task.

And why would we want to split a hair? It seems like a useless, time-wasting task with no apparent benefit.

So when we split hairs, we are engaging in a difficult task with little apparent benefit. Another similar metaphor is "counting how many angels can dance on the head of a pin."

The English language is full of words that are near synonyms -- that is, they can be used interchangeably in many circustances, but because their meaning has sutble differences cannot be used as synonyms in all circumstance. Speak and talk are an example.

This results from the history of the language. English is quite happy to borrow words from other langauges, especially words that express something in a slightly different way.