With regards to the effects of sins upon the ability of the student of knowledge to memorise, ‘Abdus Salaam ibn Burjis (d. 1425 AH) rahimahullaah said:
Disobeying Allaah, the Most High, is an obstacle to attaining Sharee’ah knowledge – because it (Sharee’ah knowledge) is a noor (light) from Allaah which He casts into the hearts of whomever He wishes from His servants.
And noor (light) and dhulmah (darkness) do not come together in a heart.
Therefore ibn Mas’ood radi Allaahu ‘anhu said:
Indeed I consider that a man (might) forget knowledge which he has already learned because of a sin which he does.
And may Allaah have mercy upon ash Shaafi’ee who said:
I complained to Wakee’ about my memorisation being bad
So he directed me to leave off sins
And he informed me that knowledge is a noor (light)
And the light from Allaah is not bestowed upon a person who is sinful
Quoted in ‘Awaa-iq ut talab of ‘Abdus Salaam ibn Burjiss rahimahullaah page 38, translated by Nasser ibn Najam
With regards to the student of knowledge needing to have a teacher, the Shaykh Muhammad ibn Saalih al ‘Uthaymeen rahimahullaah comments:
And there is no doubt that the teachers will be questioned about the students because they are their shepherds; and every person is a shepherd and will be questioned about his flock.
The students are in need of the teachers and the scholars with regards to direction and guidance because the scholars have gained experience from matters which the students have not. And with them are (aspects) of knowledge which the students do not have.
Therefore the student is in need of the teacher from the aspect of knowledge and the aspect of actions (which bring about) experience.
Thus it is binding upon him to have the utmost eagerness to select the teachers who are known for knowledge and who are known for trustworthiness and religion, and known for their sound methodology and for their tending (to matters) in a correct way such that he can take from their knowledge firstly, then from their manhaj secondly.
Quoted in Wasaayaa wa tawjeehaat li tullaab il ‘ilm pages 199-200 by Nasser ibn Najam
Shaykh Muhammad ibn Saalih al Uthaymeen stated:
Therefore it is a must for the student of knowledge to act upon (his) knowledge. So if he does not act, then knowledge becomes a harm upon him and a proof against him. And therefore the Prophet ‘alaihis salaatu wassalaam said:
The Qur-aan is a proof for you or against you.
And know that if you act upon knowledge, you will be earning worship and an increase in your knowledge because Allaah says:
And as for those who accept guidance, He (Allaah) increases them in guidance and bestows upon their taqwaa.
SoorahMuhammad (47) aayah 17
So (as for) knowledge, then Allaah certainly increases people by it and He lowers others. So whoever seeks knowledge forAllaah, obeying His command and wishing to sincerely advise His servants –Allaah will raise him.
Allaah, the Most High, said:
Allaah raises in degree those of you who believe and those who have been granted knowledge.
Soorahal Mujaadilah (58) aayah 11
Therefore I urge you, my brothers, upon acting upon knowledge such that it becomes light for you and a means of increase by which you may be guided.
(Quoted in Wasaayaa wa tawjeehaat li tullaab il ‘ilm p142, translated by Nasser ibn Najam)