The major problem with most learners, after they have acquired a substantial quantity and quality of knowledge, is failing to act with what they have acquired.
Those who learn without acting with knowledge have a great semblance with the Jews. The Jews are majorly regarded as people under the Anger of Allaah for their knowing the truth and not following it.
Many people are not blessed in their knowledge simply because they fail to act with it. When you see them you don't see the aura and awe of knowledge with them.
Allaah the Mighty blamed such people:
كَبÙرَ مَقتًا عÙندَ اللَّه٠أَن تَقولوا ما لا تَÙعَلونَ
"Most hateful to Allaah is that you say what you do not."
[As-Saff: 3]
The Salaf - which we all claim to follow - would act with what they knew.
Ibn Mas'ud - radiyallaahu an'hu - said:
'When we learnt ten verses, we would not proceed until we knew their meanings and put them into action.' (Tafseer Ibn Katheer 1/2)
Alee bn Abee Taalib - radiyallaahu an'hu - said:
يهت٠العلم بالعمل، Ùإن أجابه وإلا ارتØÙ„
'Knowledge calls out to action, if the latter hearkens to the call good, otherwise it would go away.' (Jaami Ibn Abdilbaar 2/11)
The meaning of that is knowledge and action are two inseparable companions, if you take one away from the other, the one remaining will run away too.
Not acting with knowledge is a proof against its possessor on the Day of Resurrection.
Acting with knowledge is an act of cleansing for it.
Bishr al-Haafee - rahimahullaah - said:
أدوا زكاة الØديث: Ùاستعملوا من كل ماءتي Øديث خمسة Ø£Øاديث
'Pay the right due from hadeeth (you memorize): from every two hundred hadeeth act with five hadeeth. (Adab Imlaa Wal Istimlaa p.110)
Acting with knowledge helps on its retention. Look at morning and evening words of rembrance as an instance. Whoever is constant at them would very soon memorize all the invocations said therein.
What remains of knowledge is little, and this little knowledge is found with few people, and just few people act with this little knowledge left.
Al-Imaam Adh-Dhahabee - rahimahullaah - said:
وأما اليوم Ùما بقي من العلوم القليلة إلا القليل ÙÙŠ أناس قليل. ما أقل من يعمل منهم بذلك القليل! ÙØسبنا الله ونعم الوكيل
'As for today, what remains of this little knowledge is little, and this is found with few people. And what a few number of people act with that little knowledge! Allaah is indeed sufficient for us, He is the Best to place trust. (Tadhkiratul-Hufaadh 2/1031)
You will wonder what Al-Imaam Adh-Dhahabee - rahimahullaah - would have said if he sees the people of our own time.
HasbunaLlaah wa ni'mal wakeel.
O Allaah grant us steadfastness in Your Deen.
