Another very important piece of information the Qur'an gives us about man concerns his "soul" (an-nafs). The "soul," as commonly used in the Qur'an, means "ego" or "one's personality."
In the Qur'an, Allah explains the two aspects of soul: the one inspiring evil and wicked deeds, and the other, guarding against every inculcation of evil. The Qur'an explains this in Surat ash-Shams:
By the Soul, and the proportion and order given to it; and its enlightenment as to its wrong and its right; truly, he succeeds that purifies it, and he fails that corrupts it! (Surat ash-Shams: 7-10)
As is evident from the above verses, evil exists in every man's soul. However, he who purifies his soul will attain salvation. Believers do not surrender their selves to the evil in their soul; they simply avoid it with the guidance of Allah's inspiration. As the Prophet Yusuf (as) said: "Not that I am free from sin: man's soul is prone to evil-except his to whom my Lord has shown mercy…" (Surah Yusuf: 53), provides the right manner of thinking for a believer.
Since the soul "is prone to evil," a believer must always remain vigilant about his soul. As the Prophet Muhammad (saas) also said, "the greatest struggle is the struggle against one's self (nafs)." The soul unceasingly tempts a person and never earns him Allah's approval. As it does all these things it tries to present alluring alternatives. A believer, however, thanks to his fear of Allah, is not deceived by this "misleading" attribute of the soul. He always turns towards what is right to lead a life in compliance with Allah's Will. Such is the attitude of a wise person as opposed to a foolish one, as the Prophet (saas) said:
A wise person is one who keeps a watch over his bodily desires and passions, and checks himself from that which is harmful and strives for that which will benefit him after death; and a foolish person is one who subordinates himself to his cravings and desires and expects from Allah the fulfilment of his futile desires. (Tirmidhi)