With regards to the student of knowledge not chasing after the luxuries and comforts of this world, Shaykh Muhammad ibn Saalih al ‘Uthaymeen rahimahullaah comments:
(The author’s advice), “do not accustom yourself to comfort and luxury”.
This is advice to be said to the student of knowledge and (also) to other than the student of knowledge – because accustoming oneself to that is contrary to the guidance of the Prophet sall Allaahu ‘alaihi wa sallam. For indeed he used to forbid from an abundance of luxuriousness and he would command with walking barefoot sometimes.
And a person who has become accustomed to a luxurious life will find it difficult when he encounters (certain) matters – because sometimes there will come to him matters in a form where he is not able to have the luxury (he is used to) along with him.
And let us strike an example, with the example which we have mentioned in the hadeeth: he would command with walking barefoot sometimes. Some people do not walk barefoot – always there is a sock upon him, and upon it a leather sock, and upon it a shoe. You will not find him walking, this man, if a temporary impediment were to occur to him and he were to be told to walk 500 metres without any protection for the foot; you would find that extremely difficult upon him. And sometimes his foot would bleed from the contact with the ground.
However if he were to accustom himself to a roughness and to leaving off always having comfort, then he would attain much good.
So if the (person’s) body is not accustomed to the like of these matters (of forsaking luxury), then he will have no manaa’ah (strength and toughness). You will find him feeling pain from anything from that (affair which is difficult).
However if he has manaa’ah then he will not be bothered by it.
(Sharh hilyah taalib il ‘ilm p43 of Shaykh Muhammad ibn Saalih al ‘Uthaymeen rahimahullaah, translated by Nasser ibn Najam)