Abu Musa رضی اللہ عنہ reported: The Messenger of Allah صلی اللہ علیہ وسلم said, "The guidance and knowledge with which Allah has sent me are like abundant rain which fell on a land. A fertile part of it absorbed the water and brought forth profuse herbage and pasture; and solid ground patches which retained the water by which Allah has benefited people, who drank from it, irrigated their crops and sowed their seeds; and another sandy plane which could neither retain the water nor produce herbage. Such is the similitude of the person who becomes well-versed in the religion of Allah and receives benefit from the Message entrusted to me by Allah, so he himself has learned and taught it to others; such is also the similitude of the person who has stubbornly and ignorantly rejected Allah's Guidance with which I have been sent.'' [Al-Bukhari and Muslim]
This Hadith has already been mentioned, and is repeated here to highlight the eminence of knowledge and to induce Muslims to gain it. We learn from this Hadith that there are three categories of people. First, those who acquire knowledge of the Qur'an and Hadith, act upon it and also impart it to others. Such people benefit from this knowledge themselves and extend this benefit to others also. By virtue of this quality they are the best of all. Second, those people who acquire knowledge and impart it to others, but do not fulfill the requirements of that knowledge. Such people are inferior in rank to the people of the first category and can be taken to task for their omissions. Third, those who shun the knowledge of the Qur'an and Hadith. Neither they study and hear the two themselves for their own benefit, nor do they acquire knowledge to impart it to others for their benefit. This is the worst category of people. Every Muslim should try to be in the first category of the people.