"what it is to <do something>"

Question

According to this passage, based on Three Days to See by Helen Keller:

"I do not know what it is to see into the heart of a friend through that "window of the soul," the eye. I can only "see" through my finger tips the outline of a face. I can detect laughter, sorrow, and many other obvious emotions. I know my friends from the feel of their faces. But I cannot really picture their personalities by touch. I know their personalities, of course, through other means, through the thoughts they express to me, through whatever of their actions are revealed to me. But I am denied that deeper understanding of them which I am sure would come through sight of them, through watching their reactions to various expressed thoughts and circumstances, through noting the immediate and fleeting reactions of their eyes and countenance."

1. What does the first sentence mean? ("I do not know what it is to see into the heart of a friend through that "window of the soul," the eye.")
2. Does "it" refer to the eye?
3. It seems that "what" is the object of noun clause, but heart is the object of the verb "see into", so we don't need what when we can use that. Am I making mistake?

Finally, my interpretation of this sentence may help you impart my problems:

I do not know what eye understands from people's hearts because I have never tasted the use of the eye.

Since I am not native English speaker, I apologize for my grammatical errors.

Answer 1

"I do not know what it is to see into the heart of a friend through that "window of the soul," the eye."

In this sentence, "it" actually refers to the entire phrase "to see into the heart of a friend...through the eye". The author's use of the phrase "it is" is effectively another way of saying "it means". Rearranging her words and paraphrasing hopefully makes her meaning with "it" slightly more clear. What she's basically telling us is:

"Seeing into my friend's heart with my own eyes, it (the bold phrase) is something I have never done". Obviously the author, Helen Keller, couldn't do that (it), as she was famously deaf and blind).

It looks to me like your interpretation of what she's meaning is basically correct.