Al-Hijr 15:12

The Idolators of Every Nation made a Mockery of their Messengers

Consoling His Messenger for the rejection of the disbelieving Quraysh, Allah says that He has sent Messengers before him to the nations of the past, and no Messenger came to a nation but they rejected him and mocked him. Then He tells him that He lets disbelief enter the hearts of those sinners who are too stubborn and too arrogant to follow His guidance.

(Thus We allow it to enter the hearts of the guilty.) Anas and Al-Hasan Al-Basri said that this referred to Shirk.

(and already the example of the ancients has gone forth.) meaning the destruction wrought by Allah on those who rejected His Messengers, and how He saved His Prophets and their followers in this world and in the Hereafter, is well known.

A Lexical Note of Explanation

The word: اَلشِيَعِ in the first verse (10) is the plural form of: شِیعہ (shah) which means the follower or helper of a person. Then, it is also used to denote a group which agrees upon particular beliefs and theoretical assumptions. So, the sense of the statement is that Allah Ta’ ala has sent messengers among every group or sect. Here, by using the word: فِی in فِي شِيَعِ الْأَوَّلِينَ ( in place of اِلٰی : ila: to (translated as 'among the groups of earlier peoples' ), the hint given is that the messenger for every group was sent from among that particular group so that people would find it easy to trust him, and that he too, by being aware of their taste and temperament, could make appropriate plans to work for their reform.