Why "of" ??

Hi ~

Look at the below:

Many scientists, engineers, and technical professionals have contributed to this book. Of particular help have been the book's reviewers: ...


Of particular.. what is the meaning of "Of" between sentences...

I can't understand.. just wonder your opinions..

Thanks in advance.

I don't think there's any special significance. It could have been written:

"The book's reviewers: xx xx xx xx .. xxx have been of particular help."

If the list of reviewers is extensive, perhaps the author wanted the list at the end of the sentence rather than the middle, so they just moved the "Of particular help have been" to the front.

thank you very much Friend !!

The second sentence is the same had you said:
The book's reviewers have been *of* particular help...

ablative use of 'of'

don't know what else to tell you
hope that helps