In The Name of Allaah, The Most Merciful, The Bestower of Mercy.
Allaah [The Most High] said:
وَمِنۡ أَهۡلِ ٱلۡكِتَـٰبِ مَنۡ إِن تَأۡمَنۡهُ بِقِنطَارٍ۬ يُؤَدِّهِۦۤ إِلَيۡكَ وَمِنۡهُم مَّنۡ إِن تَأۡمَنۡهُ بِدِينَارٍ۬ لَّا يُؤَدِّهِۦۤ إِلَيۡكَ إِلَّا مَا دُمۡتَ عَلَيۡهِ قَآٮِٕمً۬اۗ ذَٲلِكَ بِأَنَّهُمۡ قَالُواْ لَيۡسَ عَلَيۡنَا فِى ٱلۡأُمِّيِّـۧنَ سَبِيلٌ۬ وَيَقُولُونَ عَلَى ٱللَّهِ ٱلۡكَذِبَ وَهُمۡ يَعۡلَمُونَ
Among the people of the Scripture is he who, if entrusted with a Cantar [a great amount of wealth, etc.], will readily pay it back; and among them there is he who, if entrusted with a single silver coin, will not repay it unless you constantly stand demanding, because they say: ‘’There is no blame on us to betray and take the properties of the illiterates (Arabs).” But they tell a lie against Allah while they know it. [3:75]
Imaam As-Sadi [rahimahullaah] said: They made corrupt claims and held repulsive views, and thus considered themselves to be possessors of great status and that the illiterate Arabs were extremely degraded; therefore, the rights of the illiterate Arabs could be violated. So, through these corrupt claims and repulsive views they ate haraam and considered it lawful by way of creed.
Likewise, they lied against Allaah because the scholar who declares things lawful or unlawful is considered- by the people- as one transmitting Allaah’s Judgement and not from himself; and that [ruling of theirs about the wealth of the illiterate Arabs] is a lie. Allaah said: [وَيَقُولُونَ عَلَى ٱللَّهِ ٱلۡكَذِبَ وَهُمۡ يَعۡلَمُون – But they tell a lie against Allah while they know it]. This is one of the greatest sins-speaking about Allaah without knowledge. 
Allaah [The Exalted] said:
إِنَّ فِرۡعَوۡنَ عَلَا فِى ٱلۡأَرۡضِ وَجَعَلَ أَهۡلَهَا شِيَعً۬ا يَسۡتَضۡعِفُ طَآٮِٕفَةً۬ مِّنۡہُمۡ يُذَبِّحُ أَبۡنَآءَهُمۡ وَيَسۡتَحۡىِۦ نِسَآءَهُمۡۚ إِنَّهُ ۥ كَانَ مِنَ ٱلۡمُفۡسِدِينَ
Verily, Fir’aun (Pharaoh) exalted himself in the land and made its people sects, weakening (oppressing) a group (i.e. Children of Israel) among them, killing their sons, and letting their females live. Verily, he was of the Mufsidoon]. [Surah Al-Qasas. Aayah 4]
Imaam Al-Aloosee [rahimahullaah] said: [وَجَعَلَ أَهۡلَهَا شِيَعً۬ا – and made its people sects]- Meaning: He divided them into different sects and they went along with him in everything he desired of evil and corruption, or he used some as a means to get others to obey him; or he made them into different distinct groups under his service and used every group in some type of work, such as construction, tillage, earthwork [drilling etc] and other burdensome work, and whoever did not work was beaten, so they served him by doing so; or he made them into sects and incited hatred and enmity between them, so that they do not come to an agreement [or become united in their stance against him]. 
[Ref 1: Source: An Excerpt from Tayseer Al-Kareem Ar-Rahmaan Fee Tafseer Kalaam Al-Mannaan of Imaam Sadi (rahimahullaah)]
[2: An Excerpt from ‘Roohul Ma’aanee’ 11/64-65. Slightly paraphrased]