When does a scholar become qualified for purification and education, and is it sufficient for this methodology to be derived from the books of the scholars?

The questioner : The first question, O Shaykh, is when does a scholar become qualified for purification? And must this scholar who is qualified for purification receive the principles of purification and attain the qualification for purification from great scholars, or is it through his own independent reasoning, for example, by acquiring books of all kinds and devoting himself to them so that he becomes one who purifies? And if he purifies, will the Ummah and the scholars accept that from him? This is the first question.

The Shaykh : In any case, I draw your attention to the fact that the problem of the Muslim scholar today, regarding the knowledge whose purification is obligatory, is too vast for one scholar to handle. There must be scholars in the Muslim society; I do not mean by the tens or hundreds, but by the thousands. Each one must perform this duty of scholarly purification in the environment in which he lives. I hope no one understands from your question that one scholar in the world can perform this duty. That is impossible, because first, the scope of knowledge is very, very wide, as that scholar the Rajiz said: "Knowledge, if you seek it, is vast, and life is too short to acquire it all, so prioritize the most important of it over the next most important."
You know, for example, today there is the science of Tafsir, the science of Hadith, the science of Fiqh, and the science of language. These four sciences are necessary for a Muslim to be able to perform what I hinted at or referred to earlier regarding the obligation of purifying knowledge. But in each of these four sciences, there are at least individuals who must specialize, each in one field of these sciences. And as is very clear, it is inconceivable that one person would be a specialist in Tafsir, a specialist in Hadith, and a specialist in Fiqh, especially since what is called today comparative Fiqh has many, many branches. And also to be a specialist in language. These scholars must each work in their field of specialization and cooperate with one another to achieve what we called earlier purification. Therefore, we should not imagine that there is one person to whom the entire Ummah must submit to the leadership of his thought and knowledge alone. Rather, here and there, and throughout the world, there are individuals among the scholars who follow one methodology, the methodology of the Book, the Sunnah, and the Salaf al-Salih. Those who are below them in knowledge should follow them. This is the way to achieve purification and education. It is not possible for one person to perform the duty of purification alone, let alone purification and education! I say now, suppose a person in a certain village takes charge of purifying an aspect of knowledge in which something foreign has entered. But this person may not be able to gather the people and educate them in this purified Islam. There must be an assistant for him who receives this purified knowledge and then educates the people upon it. And so this very important matter, which is purification and education, is achieved through the cooperation of Muslim scholars in all parts of the world to achieve scholarly purification, and then the cooperation of others who have been refined by their refinement and learned by their teaching to achieve the education we are discussing. This is with regard to the answer to the first question. What is the one after it?