Is it permissible to explain and summarize a book and attribute it to its author without his permission, and is the money earned from that lawful?

Explaining a book, attributing it to its author, and receiving financial compensation for it is permissible and does not require the author's permission. This is because it is considered an independent composition, according to the definitions of authorship which include explaining what is abstruse, and the classifications of Hajji Khalifa.