Sayyidi wa sanadi Mawlana Mohammad Taqi Usmani (Allah preserve him and allow us to benefit from him a lot. Ameen!) gives the following invaluable advice to those interested in classic Sufi works:
“A point never to be forgotten when reading the books of venerable Sufi masters is that the things to acquire from them are;
– the special relationship with Allah (ta’aluq ma’Allah),
– remembrance and contemplation of hereafter,
– turning to Allah with humility (inabat),
– recognizing the plots & deceptions of nafs and methods to prevent them,
– methods of cleansing the heart and
– love of Allah and His messenger صلی اللہ علیہ و الہ وسلم.
As far as the fiqh (Shariah juristic rulings) and kalam (science of logic and art of reasoning) issues, historic events and narrations (rewayat) are concerned these are neither their (i.e. Sufi masters) field of specialization nor one can rely on them solely in these matters.
لکل فن رجال”