Essay for CAE - book review

2017 is (just) the fiftieth anniversary of the death of Lorenzo Milani, a quite a well-known priest in Italy. He's Hi is (he's is too informal for this type of text I think) famous for his commitment towards a spare (meaning not clear in this context) group of distressed kids living in the mountains and for his efforts to give them back dignity through a very unconventional school he settled set up for them.
Having already read different books about him, including a long and exhaustive biography and a collection of his letters, I didn't expect anything new from the book written by Eraldo Affinati: "Lorenzo Milani, the man of the future". Little did I know that this book would lead me to a deeper understanding of this out of the ordinary priest, especially when focusing on his childhood and on his familiar family background. The book describes in details the strong relationship with his mother, who despite being Jewish and not religious, accepted his unexpected conversion to Catholicism and his vocation to the priesthood.
Not only the author gave me a new insight on (Not only did the author give me a new insight into)  Lorenzo Milani's upbringing and on his relatives, but through the pages of his book, I got a clearer idea of his legacy to today's society. As Eraldo Affinati is a teacher himself, his analysis of Milani's passionate quest for justice through education is founded on a deep knowledge of our educational system and of his it's pitfalls. Many of the injustices and barriers that Milani wanted to knock down are still present today, even if with a different appearance. Exclusion doesn't strike poor Italian shepherds anymore, but it keeps young migrants and refugees at the margins of society.

Just - not incorrect here, but it does suggest meanings you may not intend, like it could mean 'almost' or 'only' - as though you would expect it was much longer than 50 years.

'Familiar' is ambiguous here, and 'family' much clearer I think. 

'Not only the author gave me'  I can't explain why but 'Not only did the author give me' reads more correctly to me. 

We have thoughts 'on', but insight 'into' 

A very well written essay, excellent English, and interesting subject. I enjoyed reading it and would like to find out more about him.