Commentary Among the Pious Early Generations
The first thing to know is that the Prophet ﷺ explained the meaning of the Quran to his Companions just as he taught them its words. The Divine command—Thus you shall make clear to all people what has come down to them (Sûrat Al-Na ḥl, 16:44)—calls for the former just as it calls for the latter.
The Companions report that whenever they learned ten ayât of the Quran from the Prophet ﷺ, they would not proceed further until they had understood the ideas and regulations those verses contained. The Companions used to say: “We learned the Text of the Quran and studied its ideas and injunctions all at the same time.” This explains why some Companions spent such a long time learning even one surah of the Quran.
Anas said: “We would hold in great esteem one who learned the [first] two sûrahs of the Quran, Al-Baqarah and Âl ʿImrân.” Ibn ʿUmar spent many years (eight full years, according to Mâlik) learning these two surahs.
In this approach to the Quran, the Companions were submitting to the commands of Allah in His statement: A most blessed Book have We sent down to you, so let those who hear its tidings reflect on its verses (Sûrat Ṣâd, 38:29); and also His statement: Will they not, then, reflect upon the Quran? (Sûrat Muhammad, 47:24); and again His statement: Do they not then reflect on the Word [of Allah] (Sûrat Al-Mu’minûn, 23:68).
The Primacy of Understanding What Is Read
Obviously, you cannot contemplate words unless you understand their meaning. That is why Allah has said: We have, indeed, sent it down as an Arabic Quran, so that you may understand (Sûrat Yûsuf, 12:2), and to understand the Quran means to comprehend its meaning.
Everyone knows that a book is meant, not just for [mechanical] reading, but for understanding. This is all the more true of the Quran. No one ever reads a book on a subject (medicine, mathematics, and the like) without trying to understand it. The same is true of the Quran on which rests our wellbeing and happiness, our religion and life.
This is why the Companions of the Prophet ﷺ differed little in their critical explanation of the Quran. Their Successors (Al-Tâbiʿîn) have differed somewhat more. Their differences, however, are negligible compared to those of the latter generations. As a rule, the better a generation of Muslims is, the more profound is its understanding and knowledge of the Quran, and the greater is the agreement of its scholars on its critical explanation (tafsîr).
Among the Successors there were many who studied the whole Quran with the Companions. For instance, Mujâhid studied the entire Quran, as he himself said, with Ibn ʿAbbas, questioning him about each and every verse and noting all his comments.
That is why Al-Thawrî said: “If you get the comments of Mujâhid, they are sufficient.” This also explains why Al-Shâfiʿî, Al-Bukhârî, Imâm A ḥmad, and others who have commented on the Quran, quote Mujâhid more than any other commentator.
The point I am emphasizing is that the Successors learned the critical explanation (tafsîr) of the Quran from the Companions, even as they learned the ḥadîth of the Prophet ﷺ from them. This in no way is meant to deny that they exercised their minds and expressed their opinions on various ayât, just as they did with regard to various a ḥâdîth of the Prophet ﷺ.