The Apostle Paul describes the war within him that is waged between the Spirit and the flesh. It is a very real battle. He saw the rottenness of the flesh. It is corrupt and evil. He calls this the sin that dwells in him. He saw also the Spirit prompting him not yield to sin. He could differentiate well between good and evil and he realizes the pull toward evil is such a contending force within him. This acknowledgment leads him to endeavour by prayer and supplication to keep close to God and not yield to sin.