وَإِذْ أَخَذَ اللَّهُ مِيثَاقَ الَّذِينَ أُوتُوا الْكِتَابَ لَتُبَيِّنُنَّهُ لِلنَّاسِ وَلَا تَكْتُمُونَهُ فَنَبَذُوهُ وَرَاءَ ظُهُورِهِمْ وَاشْتَرَوْا بِهِ ثَمَنًا قَلِيلًا ۖ فَبِئْسَ مَا يَشْتَرُونَ
[[Meaning: And remember when Allaah took a covenant from those who were given the Scripture to make it clear to the people, and not hide it; but they cast it behind their backs, and they purchased thereby some paltry gain. So evil is that which they purchased.]] [Soorah Aali `Imraan (3): 187]
Shaikh `Abdur-Rahmaan ibn Naasir as-Sa’dee- rahimahullaah-said in his Tafseer of the Aayah:
“The Covenant (al-Meethaaq) is the weighty, emphatic covenant; and Allaah-the Most High-took this Covenant from everyone to whom He gave the Book, and whom He taught knowledge to; that they should clarify to the people whatever they are in need of from that which Allaah taught him, and that they should not hide that, nor be miserly with them regarding it – particularly if they ask him about it, or when something occurs which necessitates that. So in such a situation it is obligatory upon everyone who possesses knowledge that he clearly explains it to the people, and clarifies the truth from falsehood. So as for those guided to correctness by Allaah, then they carry this out in the most complete manner, and they teach the people that which Allaah has taught them, seeking the Pleasure of their Lord, and out of compassion for the creation, and from fear of the sin of hiding the truth.
As for those who were given the Scripture, from the Jews and the Christians and their like, then they cast this agreement and this covenant behind their backs. They took no notice of it. So they hid the truth and they put forth falsehood. They boldly violated the prohibitions laid down by Allaah; and they neglected the rights of Allaah and the rights of the creation. Through concealing the truth they purchased a paltry gain- which is what they acquire, if they acquire anything, from positions of authority and trivial wealth; from their lowly ones- from those who follow their desires, and who give precedence to their desires over the truth.
فَبِئْسَ مَا يَشْتَرُونَ
[[Meaning: So evil is that which they bought]]:
since it is the most wretched exchange. They turned away from clarifying the truth, which is something which brings about eternal bliss, and religious and worldly benefits – the most tremendous and exalted goals. So they only chose that which is lowly and despicable over that which is lofty and precious because of their wretchedness and degradation, and because they are not fitting for anything other than that which they were created for.”
 Taken from “Tayseerul-Kareemir-Rahmaan fee tafseer Kalaamil-Mannaan” of Shaikh AbdurRahmaan ibn Naasir as-Sa’dee.
[Translated by Aboo Talhah Daawood ibn Ronald Burbank -rahimahullaah]