Allah has exhorted man to curb the urge to sin. Man has to obey Allah and become His slave because Allah has created man and not the nafs. This indicates that the urge to sin is essential. That is why He is commanding us to prevent the nafs. Had there been no urge to sin, taqwa would not have existed because taqwa means to subdue the urge of the nafs to sin and to endure the grief that follows.