وَمِنْ قَبْلِهِ كِتَابُ مُوسَى إِمَامًا وَرَحْمَةً وَهَذَا كِتَابٌ مُصَدِّقٌ لِسَانًا عَرَبِيًّا لِيُنْذِرَ الَّذِينَ ظَلَمُوا وَبُشْرَى لِلْمُحْسِنِينَ ﴿۱۲﴾ إِنَّ الَّذِينَ قَالُوا رَبُّنَا اللَّهُ ثُمَّ اسْتَقَامُوا فَلَا خَوْفٌ عَلَيْهِمْ وَلَا هُمْ يَحْزَنُونَ ﴿۱۳﴾ أُولَئِكَ أَصْحَابُ الْجَنَّةِ خَالِدِينَ فِيهَا جَزَاءً بِمَا كَانُوا يَعْمَلُونَ ﴿۱۴﴾

﴾12﴿ Wa min qablihee kitaabu Moosaaa imaamanw-wa rahmah; wa haazaa Kitaabum musad diqul lisaanan 'Arabiyyal liyunziral lazeena zalamoo wa bushraa lilmuhsineen
﴾13﴿ Innal lazeena qaaloo Rabbunal laahu summas taqaamoo falaa khawfun 'alaihim wa laahum yahzanoon
﴾14﴿ Ulaaa'ika Ashabul Jannati khaalideena feehaa jazaaa'am bimaa kaano ya'maloon

﴾12﴿ And before this, the Book of Moses (was revealed) as a guide and mercy. And this (Qur'an) is a confirming book in the Arabic language, to warn the wrongdoers and give glad tidings to the doers of good
﴾13﴿ Indeed, those who say, "Our Lord is Allah" and then remain steadfast (in faith), they will have no fear, nor will they grieve
﴾14﴿ These are the people of Paradise, wherein they will abide forever, rewarded for what they used to do

[12] This is a transmitted proof and an encouragement toward the Qur’an.
(Imāmā) means that it contains such clear evidences of monotheism and the truthfulness of the Final Messenger that following it is necessary.
(Wa raḥmah) means that it contains such beliefs, matters, and rulings that they are themselves manifestations of Allah’s mercy. Likewise, acting upon it becomes a means of attaining Allah’s special mercy.
[13,14] Up to this verse, the states of the deniers were mentioned, along with warnings and responses directed at them. Now, the qualities of the believers are being described, and for them, there is glad tidings.