What is meant by knowledge and reason in the verses that describe disbelievers as not knowing or not reasoning, what are the conditions for sound knowledge in Islam, and does that prevent benefiting from the knowledge of disbelievers?

The verses describing disbelievers as not comprehending or not knowing indicate that their worldly intellect and knowledge are useless to them as long as they do not guide them to what is right, nor lead them to Allah. They deny the Resurrection and deem the raising of bodies impossible despite the clarity of the rational argument.

This meaning is confirmed by the conjunction of the negation of guidance with expressions of a lack of comprehension or knowledge in verses such as: "Even if their fathers knew nothing and were not guided?" [Al-Ma'idah:104], and "Deaf, dumb, and blind — so they do not comprehend." [Al-Baqarah:171], and "They are not but like livestock; rather, they are more astray in [their] way." [Al-Furqan:44], and "They have hearts with which they do not understand, and they have eyes with which they do not see, and they have ears with which they do not hear. Those are like livestock; rather, they are more astray." [Al-A'raf:179], and "Had we listened or reasoned, we would not have been among the companions of the Blaze." [Al-Mulk:10].

Sound knowledge is stipulated to be beneficial. It must not be among the forbidden sciences, such as magic and astrology, nor should it be intended for a malicious purpose. If religious knowledge is acquired for show and reputation, it will be a burden upon its possessor, as mentioned in the Hadith of Abu Hurairah about the first people with whom Hellfire will be kindled.

This does not preclude benefiting from the worldly sciences of disbelievers that are useful to Muslims in their daily lives, livelihoods, economies, weaponry, and so forth. A Muslim is rewarded for learning them if they purify their intention and aim for reform.