Allah - Most Perfect, Most High - said:
"O you who Believe! Have taqwa (fear) of Allah and believe in His Messenger; and He will bestow upon you a double portion of His Mercy and He will provide you with a light by which you will walk."Allah - the Most High - also said:
"O you who Believe! If you have of taqwa of Allah, He will give to you a Furqan (criterion to judge between right and wrong)."AlHafidh Ibn Kathir (d. 777H) - rahimahullah - said:
"Ibn 'Abbas, As-Suddi, 'Ikrimah, Ad-Dahhak, Qatadah and Muqatil ibn Hayyan all said about Furqan that it means: a way out (from difficulty). Mujahid added: A way out (from difficulty) both in this world and in the Hereafter. In a narration from Ibn Abbas he said it means: salvation; and in another narration from him: being helped. Muhammad ibn Ishaq said that it means: a criterion to judge between truth and falsehood. This explanation from Ibn Ishaq is the most general of what has already preceded and it is a necessary consequence of it. Since whoever has taqwa of Allah by obeying His command and abandoning what He has prohibited, will be given the ability to recognise truth from falsehood. This will be the cause for his salvation, his being helped; and the cause for his worldly affairs being made easier and his happiness on the Day of Judgement. It will also be the cause for his sins to be expiated by Allah and his being granted forgiveness and shielding him from the people. It will likewise be the cause of him being the recipient of a great reward from Allah as He - the Most - says:
'O you who Believe! Have taqwa (fear) of believe in His Messenger; and He will bestow upon you a double portion of His Mercy and He provide you with a light by which you will walk.'
Ibn Masud - radhiallahu 'anhu - said, "Indeed I hold that a person forgets knowledge that he used to know because of sins that he commits."{qluetip title=[2]}Related by Waki' in Az-Zuhd (no.329) and its isnad is Sahih{/qluetip}
Waki (d. 197H) - rahimahullah - said, "I seek help in memorization by abandoning sin and disobedience."{qluetip title=[3]}Related by Ibn Hibban in Rawdatul-'Uqala (p. 39){/qluetip}
Malik (d. 179H) said to Ash-Shafi'i when they first met, "Indeed I see that has placed a light upon your heart, so do not extinguish it with the darkness of disobedience and sin."{qluetip title=[3]}A'lamul-Muwaqqi'in (4/258) of Ibn AlQayyim{/qluetip}
Imam AshShafi'i (d. 204H) - rahimahullah - said, "Whosoever loves that Allah should open-up his heart for him and grant light to him, then let him abandon speech about that which does not concern him, and abandon sins and turn away from acts of disobedience. Then there will be between him and Allah a hidden treasure of good actions. So if this is done, then Allah will open up such knowledge for him, that will preoccupy him. And indeed in death is the greatest pre-occupation."{qluetip title=[4]}Related by AlBayhaqi in Manaqiush-Shafi'i (2/171){/qluetip}
Shaykh ul-Islam Ibn Taymiyyah (d. 728H) said, "Allah - the Most Perfect - has made as a punishment for people's sins, the absence of guidance and beneficial knowledge, as He says:
'They say: Our hearts are wrappedup (and we do not understand). Rather, Allah has has put a seal upon their hearts because of their disbelief.'
"And He said:
'They say: Our hearts are wrappedup (and we do not understand). Rather, Allah has cursed them for their disbelief.'
"And He said:
'And we shall turn their hearts and their sight away from guidance, as they refused to believe therein for the first time.'
"And says:
'In their hearts is a disease, and Allah increases their disease.'
"And He says:
'So when they turned away, Allah turned their hearts away.'
(s) An-Nubadh fi Adab at-Talab (pp. 12-15)