In Adam all sinned, and because of Adam's sin all men are sinners. All mankind is dead in sin. Sin caused Adam to be separated from relationship and fellowship with God. Because of sin, Adam died spiritually; therefore he could no longer have communion with God.
Romans 6:11-13 tells us that we were dead, and now in Christ we are alive. We were sinners because we were spiritually dead, and now having been born again by the Spirit, our spirits made alive, and we are children of God (I John 5:10-12). We were sinners by nature, but now in Christ we are no longer sinners. We do not have a sin nature--what was dead is now alive. We are a new creation in Christ. We are no longer in the flesh but in the Spirit, if the Spirit of Christ dwells in us.
Man's "flesh" is not sinful, nor is his body with its senses and appetites. It is only when these appetites control us that they become sinful. None of the functions of the body or soul are sinful. Paul tells us in Romans 8:4 that the requirements of the law are fulfilled in us who walk according to the Spirit.
God's Word says we are either in Adam or in Christ. There are no in-betweens. Some have said that when man is unregenerate he has only one nature but when he becomes a child of God he has two natures. But this is only speculation, not truth based on the Word of God. When we make a place for sin in the Christian's walk, we have to come up with some very strange doctrines. Man draws his own conclusions because he would rather trust in his own experience than in God's Word. He tries to find ways to justify his own feelings and experiences. We must start the other way--with God's Word--and make truth our experience.
Year after year, many are trying to "kill the old man." They don't even know what or who the old man is. There is no place for the old in the new! If we are in Christ, we are in the new creation. Christ is the new man; Adam is the old man. Romans 6:6,7 tells us that our old self ("old man") was crucified with Him so that our body of sin might be done away with, that "we should no longer be slaves to sin. For he who died is freed from sin."
In Christ we have been made alive spiritually. We have been born again by the Spirit. When man, from his heart, believes in Jesus Christ as His Lord and Savior, he is made alive in his spirit, because this is where we worship and commune with God.
Sin is really self-rule. It is the disposition that rules the life apart from God. When that rule is changed and Christ is made Lord of our lives, we are no longer sinners, nor do we continue to sin. We need to go on from here and be renewed in our minds, that we may have knowledge of God's great salvation which cannot leave us with two natures battling one another until we pass out of this body.