Where does the old sin nature operate in human beings?
The old sin nature operates in the human body—the flesh of blood, bone, and five senses. After Adam sinned, the spirit or place of fellowship was made dormant, and the sin nature now operates in that physical body, leaving humanity with no means of communication with God.
Les explains that the old sin nature operates in the body of flesh and blood and bone, which functions through the five senses. He notes that when Adam sinned, the original sin nature entered, and the spirit—the place of fellowship—was completely put out of commission, made dormant. So in our human experience, we live in that same physical body where the old personality, the sin nature, operates. Les further points out that this leaves the lost person with no means of communication with God; even a desperate cry from a foxhole is not heard unless it is a call for salvation. Romans 8 makes it plain that the unbeliever is an enemy of God, and we do not deal with an enemy in fellowship.