What is the evidence for the obligation to understand the Book and the Sunnah according to the understanding of the righteous Salaf?

The Shaykh : So where did we take this restriction from? First, we took it from some texts from the Book of Allah and from the hadith of the Messenger of Allah (peace and blessings be upon him). Second, we took it from history, which records for us the connection of the Companions of the Prophet (peace and blessings be upon him) to it from one side, and that they were pure Arabs who were closer to understanding the Book and the Sunnah from the Arabic perspective than those who come after them, especially if they are non-Arabs like us in this time. For these two reasons, the exhortation came in the Book of Allah and in the hadith of the Messenger of Allah (peace and blessings be upon him) to adhere to what this righteous Salaf was upon. For example, the saying of Allah (Mighty and Majestic): .
The point in this verse is that Allah (Mighty and Majestic) warns in it not only from opposing and contradicting the Messenger, but also warns from following other than the path of the believers: . Allah (Mighty and Majestic) mentioned here the path of the believers and warned against contradicting their path to the path of others, namely the disbelievers or the misguided.
So the question that arises now is: Allah (Mighty and Majestic) did not limit Himself in this verse to His saying (Exalted is He): , but He added to it and said: . What is the wisdom behind that? The wisdom is clear and evident, and praise be to Allah, and that is: that these believers are those who—as we indicated at the beginning of our speech—received the Qur'an directly from the mouth of the Prophet (peace and blessings be upon him), fresh and new, and then received from him the explanation that Muslims need in their time and in the times after them. So these people have a distinction that they possess exclusively over the Muslims who came after them. For this reason, Allah (Mighty and Majestic) mentioned in the verse: . It is known with certainty by every Muslim that Allah (Mighty and Majestic) does not mention a single letter in the Book of Allah in vain, far be it from Him, let alone that He mentions a sentence like this in vain . If Allah (Mighty and Majestic) had said: "And whoever opposes the Messenger after the clear proof has come to him, We will turn him to what he has turned to and We will cast him into Hell, and evil is the destination," the purpose and the wisdom and the meaning that Allah (Mighty and Majestic) wants from this verse would have been achieved. But He (Blessed and Exalted is He) intended another meaning to add to the first meaning, which is to draw the attention of Muslims in every land and in every era to paying attention to the path of the believers who were before them, and specifically the three generations attested to as the best in the mass-transmitted hadith from the Prophet (peace and blessings be upon him) that he said: . Since these people had this distinction, Allah (Mighty and Majestic) specified in that verse that it is not permissible for Muslims to contradict their path. There is no doubt that the path of these Muslims is in accordance with the speech of the Lord of the Worlds and the hadiths of His Messenger (peace and blessings be upon him), but the difference between them and those who come after them is that they are correct in their understanding for the reason we mentioned earlier, due to their closeness to the Prophet (peace and blessings be upon him) in receiving, language, and understanding.