These are some brief words about the meaning of knowledge and its classification into that which is beneficial and that which is not; as well as a note regarding the excellence of the knowledge of the Salaf over that of the Khalaf.
The way and wisdom of the Salaf, all goodness lies in traversing the way of the Salaf, beneficial Knowledge with regards the Inner Sciences, the foundation of knowledge and many other branches of the beneficial knowledge. From the signs of beneficial knowledge is that one does not lay claim to having knowledge or become boastful of it.
He does not accuse others of ignorance unless they oppose the Sunnah and its people, in which case he speaks against him out of anger for the sake of Allah, not out of personal anger or the desire of gaining ascendancy over him. As for the second category of knowledge which Allah mentioned by way of censure, examples of it can be found in his mention of magic (sihr), astronomy, the Rationalisation of the People of Opinion, debating about the religion. From those sciences that have been innovated in the discussion and analysis of the inner sciences dealing with matter such as gnosis and the actions of the heart and their ensuing implications based upon pure opinion, spiritual experience (dhawq), or spiritual realization (kashf). The same applies to delving too deeply into the science of genealogies even though it be something that is needed.
The same applies to delving too deeply into the Arabic language and indeed to do so serves to direct one away from learning more important matters and to devote oneself to it prevents one from acquiring much beneficial knowledge.
From amongst these sciences are those innovated by the Mutazila in their discussion of Qadr and setting up analogies for Allah while a clear prohibition has been mentioned against delving into Qadr. Linked to this is the innovation concocted by the Mutazila, and those who traverse their path, in their discussion of the Essence (dhat) of Allah, the Exalted, and His Attributes through the medium of rationalization.