What is the first and foremost obligation upon the slaves?

The first obligation upon the slaves is to have recognition of the purpose for which Allaah created them; and for which He took a covenant from them and the purpose for which He sent them His Messengers and revealed His Books; and for which He created this present life, the Hereafter, Paradise and Hell-fire; and for which the Inevitable would come true; and the Event would befall; and for which the Scales are set up and the Records fly; and for which there would be either happiness or misery; and according to which the lights would be divided: “And whoever Allaah gives not light, there will be no light for him” (an-Noor: 40)