You apply the Qur'aan's teachings by deeming lawful what it permits, and deeming forbidden what it forbids; by avoiding what it prohibits and acting on its commands; by applying its clear verses and believing in its unclear verses; and by applying all of its laws and precepts. A severe punishment awaits those who, despite being blessed by Allaah سبحانه و تعالى with knowledge of the Qur'aan, do not apply its teachings. In a long Hadeeth
wherein the Prophet صلى الله عليه وسلم described a dream he had, he صلى الله عليه وسلم said,
فَانْطَلَقْنَا حَتَّى أَتَيْنَا عَلَى رَجُلٍ مُضْطَجِعٍ عَلَى قَفَاهُ، وَرَجُلٌ قَائِمٌ عَلَى رَأْسِهِ بِفِهْرٍ أَوْ صَخْرَةٍ، فَيَشْدَخُ بِهِ رَأْسَهُ، فَإِذَا ضَرَبَهُ تَدَهْدَهَ الْحَجَرُ، فَانْطَلَقَ إِلَيْهِ لِيَأْخُذَهُ، فَلاَ يَرْجِعُ إِلَى هَذَا حَتَّى يَلْتَئِمَ رَأْسُهُ، وَعَادَ رَأْسُهُ كَمَا هُوَ، فَعَادَ إِلَيْهِ فَضَرَبَهُ، قُلْتُ مَنْ هَذَا قَالاَ انْطَلِقْ. (ثُمَّ فَسَّرَ لَهُ ذَلِكَ صلى اللّه عليه وسلم فَقَالَ:) وَالَّذِي رَأَيْتَهُ يُشْدَخُ رَأْسُهُ فَرَجُلٌ عَلَّمَهُ اللَّهُ الْقُرْآنَ، فَنَامَ عَنْهُ بِاللَّيْلِ، وَلَمْ يَعْمَلْ فِيهِ بِالنَّهَارِ، يُفْعَلُ بِهِ إِلَى يَوْمِ الْقِيَامَةِ
"Until we came upon a man who was lying down on his back, and upon another man who was standing over him with a rock or a stone. [The man who was standing] would break the other man's head, and when he would strike him, the rock would roll away. Whenever he went to retrieve the rock, he would not sooner return than the other man's head would heal and return to its previous state. Then the man [who was standing] would strike him [over and over again]. I asked, 'Who is this?'" The Prophet صلى الله عليه وسلم then explained the meaning of what he saw: "As for the one whose head would be [constantly] broken, he is a man whom Allaah سبحانه و تعالى taught the Qur'aan, but who would then sleep from it at night, and not apply it during the day. That will be done to him (his head being struck with the rock, over and over again) until the Day of Resurrection."   Notes:
 Bukhaaree (1386)
 Shaykh Fu'ad Ibn 'Abdul-'Azeez Ash-Shulhoob حفظه الله, The Book of Manners (Darussalam), pp. 18-19.
See also: A Muslim's Obligation Toward the Qur'an