What is the vile soul, what are its causes, symptoms, and treatment, is it innate or acquired, why did Al-Khidr kill the boy in Surat Al-Kahf, and is this evidence that there is no way for the vile soul to become good?

The wicked self is that which incites to evil. Among the signs of a wicked self or a sick heart mentioned by scholars are:

1. The inability to love Allah, prefer Him, and love the Hereafter, living like animals without purpose or worship of Allah. 2. Not feeling pain from the wounds of sins, unlike the believer for whom sin prompts repentance. 3. Not being bothered by ignorance of the truth; indeed, a person might be ignorant that he is ignorant, thereby closing the door to learning for himself. 4. Preferring harmful provisions over beneficial ones, such as listening to music and watching debased movies instead of the Qur'an. 5. Settling in this world and being content with it, making it one's greatest concern without striving for the Hereafter or aspiring to higher ranks.

Man is born upon fitra (innate disposition), and devils may lead him astray from it, but he has free will and will be questioned about his actions. Messengers were sent to complete and affirm the fitra, not to corrupt it, as Allah Almighty says: "The fitra of Allah upon which He has created mankind."