Behishti Zewar is not an entry level book. If you have not read anything at all as yet, start with smaller text. Ascent maye good. You can try Ta'leemul Haq too. Then go for Behishti. Many things in Behishti Zewar need qualified guidance for understanding. Infact it is more indepth than Nur ul Idaah. The only reason it is recomended is because of its good style and being contemporary book.