Imaam Ibn Qudaamah Al-Maqdisi rahimahullaah said:
The Ílm Al-Mua’malah (i.e the knowledge of the relationship between servant and his Lord) that a servant is charged with is classified into three divisions:
♦ Al-I’itiqaad (belief)
The first thing that is obligatory upon one is to know the two parts of the ‘Kalimatu Ash-Shahaadah’ (Laa ilaaha illallaah Muhammadu Rasulullaah)
The gravity of this obligation depends on how dangerous and risky the situation a servant faces.
From this, we understand that what is obligatory upon one is to know the obligation that is specific to one at a given situation and this is called Fardu ‘ayn.
♦ Al-Fi’l (action).
This has to do with the knowledge which people cannot do without in their day to day life.
This is called Fardu kifaayah .
Medicine, mathematics, etc, all are necessities that the ummah cannot do without, especially when it comes to health matters and sharing of inheritance respectively. And if some people were able to do that, then the obligation is uplifted from others.
But having deep understanding of these sciences is not a necessity but a virtue, unlike the knowledge of the Deen which are all praiseworthy and its deep understanding are highly needed.
♦ At-Tark (prohibition)
This is for one to know what is made Haraam in a specific situation he/she encounters and to dissociate from it immediately.
Allaahu A’alam
Baarakallaahu feekum