This is an important question for Dr. MacArthur to answer. If a believer possesses only a new nature in Christ and not an old sinful nature (as he teaches, EPHESIANS, p. 164), then it would seem that the believer would never sin because the new man "is created in righteousness and true holiness" (Eph. 4:24). MacArthur himself says, "man's new nature is holy, pure, and destined for heaven" (Freedom From Sin, p. 56). But MacArthur does not believe in sinless perfection. Commenting on Romans 6:12a, MacArthur says, "Paul was not saying that sin is no longer present in the believer. Sin is still a force to be dealt with" (Freedom From Sin, p. 55). How then does he explain sin in the life of the believer who has only a new nature? Sin must have a source. It must originate and come from somewhere. If its source is not the old nature, then where does it come from? Here is Dr. MacArthur's answer:
 

"Christians sin because of the vestiges of sinful flesh, not because they have the same old active sinful nature" (Faith Works, p. 116).

"It is not a remaining old nature but the remaining garment of sinful flesh that causes Christians to sin" (EPHESIANS, p. 164).

"Why is it that we continue to sin? The answer is that believers are not in the flesh, but the flesh is still in them! Although the flesh no longer makes you its slave, you still possess an unredeemed body, which remains susceptible to sin" (Freedom From Sin, p. 112).

"Christians and sin don't mix. Occasionally we sin because we still live in the flesh" (Marks of a True Believer, p. 58).

"Paul acknowledges that being a new self in the image of God does not eliminate sin. It is still present in the flesh, the body, the unredeemed humanness" (EPHESIANS, p.179).

"The reason believers still sin is their unredeemed flesh" [Study Bible Note under Colossians 3:10].

"There is still sin in the believer's unredeemed human flesh" [Study Bible Note under Ephesians 4:24].

"Although the old self is dead, sin retains a foothold in our temporal flesh or our unredeemed humanness" [Study Bible note under Romans 6:6].

"The flesh serves as a base camp from which sin operates in the Christian's life. Because of its fallenness, it is still subject to sin and is thoroughly contaminated" [Study Bible Note under Romans 7:18].

"There is in you a new nature which is holy, but that sinful presence of the flesh is still there" (Tape GC 45-52, Romans 7). "Sin is seated in the flesh" (Tape GC 45-53, Romans 7).

"He [the Christian] is a new, redeemed, holy creation incarcerated in unredeemed flesh" (Romans 1-8, p. 326).

"Our new nature within, which according to 1 John 3:9 does not sin. When we go against our new nature, it isn't the law that's responsible, but the sin that still resides in our frail human flesh" (Masterpiece, March/April 1990, p. 20). "After salvation, sin no longer resides in our innermost self, which is recreated to be like Christ. Yet it finds its residual dwelling in our flesh. That's why Paul said nothing good dwelt in his flesh (v.18)" (same article in Masterpiece, p. 21).

"The apostle confesses, `I know that nothing good dwells in me, that is, in my flesh' (Rom. 7:18). Even as an apostle of Jesus Christ he possessed a remnant of the sinfulness that characterizes all human beings" (Romans 1-8, p. 382).

"This residual fallenness—the flesh—is what drags us repeatedly into sin, although we hate and despise sin" (Faith Works, p. 134).

"The only residence of sin in a believer's life is his flesh, his unredeemed humanness. The flesh in itself is not sinful, but it is still subject to sin and furnishes a beachhead from which to operate in a believer's life" (Romans 1-8, p. 387).

"Paul is saying in Romans: 'Look. The old man is done away, the old nature is destroyed. Now you are free from sin's bondage.' Oh, you will mess up because of the problem of the flesh that still exists, but sin cannot lay a claim on you" (Your Completeness in Christ, p. 100).

"The real believer will obey. Because we all retain the vestiges of sinful flesh, no one will obey perfectly" (Gospel According to Jesus, p. 174).

"Paul longed for the day when he would be rescued from the last vestige of his old, sinful, unredeemed flesh" (Romans 1-8, p. 392).

"What happens when a believer sins? The new nature within him is not to blame; the sin that dwells in his body is the culprit" (Freedom From Sin, p. 39).

"The question then arises as to why believers sin if the old self is gone. They do so because the new self lives in the old body and must contend with the flesh" (Colossians and Philemon, p. 149).

"Even though we believers are limited by our earthly bodies and can therefore experience only imperfect holiness, we will nonetheless obey because we are new creatures in Christ" (Freedom From Sin, p. 70).

"The physical body [is] the headquarters from which sin operates in the believer" [Study Bible Note under Romans 6:13].

"[The moral body is] the only remaining repository where sin finds the believer vulnerable. The brain and its thinking processes are part of the body and thus tempt our souls with its sinful lusts" [Study Bible Note under Romans 6:12].

"Sin no longer controls the whole man (as with an unbeliever) but it does hold captive the believer's members, or his fleshly body" [Study Bible Note under Romans 7:14].

"THE FLESH=Our unredeemed humanness—that complex of sinful passions that sin generates through its one remaining domain, our bodies" [Study Bible Note under Romans 8:12].

MacArthur's comments on Romans 7:24 ("the body of this death"): "Where is his (Paul's) problem? It is in his body." (Tape GC 45-53).

Sin "does not reign in your new creature, your new nature, it reigns in your mortal body" (Tape GC 45-52, Romans 7).

"It is only the believer's body that remains subject to sin and death" (Romans 1-8,p. 392).

"A true Christian battles with the flesh because his mortal body still hangs on and tries to lure him back into the old sinful ways" (Romans 1-8, p. 418).

"The apostle Paul made a connection between the believer's physical body and sin....The body in Paul's terminology is the vehicle by which sin manifests itself in the believer. It is the beachhead of sin, and is where temptation strikes first....Although sin is not the product of our new self, we're still bound to some degree by the body we dwell in" (The Masterpiece, March/April 1990, p. 20).

"You say, 'But if we have had our fallen nature put away, if we have put off the body of the sins of the flesh (human nature in its fallen condition), and if we have a new nature, then why do we still sin?' The answer is that you not only have a new nature, but you also have an old body. You have a new inside and an old outside...The new nature that is in me has been purified, but the body that it lives in is a mess. When I go to heaven I don't get a new inside, I get a new outside. If I could just remove my good inside from this bad outside, I could really live...' In my new creation life the new nature is there, but surrounding it is the flesh'" (Your Completeness in Christ, pp. 96-97).
 

"Why do you sin? Because God didn't do a good job when He saved you? Because your new nature isn't complete? Because you're not prepared for heaven yet?...NO! Because sin is still there in your humanness" (Tape 45-53, Romans 7).

"Why do we sin?...It's because sin is still present in our humanness, which includes the mind, emotions, and body" (Freedom From Sin, p. 173).

"Even though regeneration produces a new disposition with holy longings, that new life force remains incarcerated within the old, unredeemed human flesh, precipitating an ongoing battle between the spirit and the flesh" (The MacArthur N.T. Commentary 1 Peter, under 1 Pet. 2:11,  p. 137).

"When you sin it isn't the new you, it's your flesh, your humanness...sin is in our humanness" (Tape GC 45-53, Romans 7).

"You say, 'But John, I have a problem. I may be a new man and there might not be any old man around and there might not be any old me around but man I got a lot of trouble because I keep sinning. Where is it coming from?' Basically it's coming because your new man is connected up with your flesh. You have to make a distinction between the flesh and the old man. The flesh is just your humanness and it's still around and it bugs the new man...You're the same new creature you're going to be forever, did you know that?...No wonder Paul says, 'I'd sure like to get out of this vile body'" (Tape GC 2147, Col. 3:9-11, 1976). (Note: According to MacArthur the source of sin has nothing to do with the old man or the old nature. The reason we sin is because our new man is connected with our FLESH and the flesh refers to our "vile body", that unredeemed part of us which MacArthur likes to call our "humanness" or our "unredeemed humanness."

"You are not less evil now than you used to be. In your unredeemed mortality and humanness you are evil" (Tape GC 45-52, Romans 7).

"The problem is 'sin that dwells in me'--its our humanness (that is the problem)" (Tape GC 45-52, Romans 7).

"Scripture uses the term FLESH in a morally evil sense to describe man's unredeemed humanness, i.e., that remnant of the old man which will remain with each believer until each receives his or her glorified body" [Study Bible Note under Romans 7:5].

"His sin does not flow out of his new redeemed innermost self, but from his unredeemed humanness, his flesh" [Study Bible Note under Romans 7:17].

"Sin is seated in the flesh and we've said before and say again that the flesh is our humanness, it isn't necessarily in and of itself evil, but it's where sin finds its base of operation" (Tape GC 45-53).

"The conflict in the life of a believer is a conflict between a new creation which is holy (the eternal seed, the real you, the basic you, the re-created you, the redeemed you) and your unredeemed mortality, your unredeemed humanity which is still present" (Tape GC 45-53, Romans 7).

"But as long as he (the Christian) remains in his mortal body, in his old unredeemed humanness, he remains subject to temptation and sin" (Romans 1-8, p. 391).

"Even though he (the believer) has been recreated and there's a new nature there, that new nature is still encased in humanness, and therein lies the struggle. So even though we are redeemed, sin hangs on in our flesh, our mortality, our unredeemed humanity" (Tape GC 45-53, Romans 7).

"A believer's unredeemed humanness remains with him until he is transformed to heavenly glory. And, as both Scripture and experience clearly teach, the remaining humanness somehow retains certain weaknesses and propensities to sin. The tyranny and penalty of sin both in and over the Christian's life have been broken, but sins potential for expression in his life has not yet been fully removed. His human weaknesses and instincts make him capable of succumbing to Satan's temptations when he lives apart from the Spirit's Word and power. He is a new, redeemed, holy creation incarcerated in unredeemed flesh" (Romans 1-8, p. 326).

According to MacArthur, the old nature is dead and gone, and the believer is a new creature and possesses only a new nature. The amazing thing is that SIN has somehow SURVIVED! But SIN has not done well in its survival! Only the remnants of sin have survived. Most of sin is gone and removed, but some remnants have survived and remain. Notice the language MacArthur uses to describe this:

"This RESIDUAL FALLENNESS--the flesh--is what drags us repeatedly into sin" (Faith Works, p. 134).

"There's a big difference between SURVIVING SIN and reigning sin" (Faith Works, p. 135).

"the REMNANTS of sin in the flesh..." (Faith Works, p. 135).

"It is not a remaining old nature but the REMAINING garment of sinful flesh that causes Christians to sin" (Ephesians, p. 164).

"[sin] finds its RESIDUAL dwelling in our flesh" (article in Masterpiece referred to above, p. 21).

"[Paul] possessed a REMNANT of the sinfulness that characterizes all human beings" (Romans 1-8, p. 382).

"Paul longed for the day when he would be rescued from the LAST VESTIGE of his old, sinful, unredeemed flesh" (Romans 1-8, p. 392).

"we all retain the VESTIGES of sinful flesh" (Gospel According to Jesus, p. 174).

"Christians sin because of the VESTIGES of sinful flesh, not because they have the old active sinful nature" (Faith Works, p. 116).

If this is really true then why did Paul say, "Oh wretched man that I am!"? Why didn't he say, "I am not very wretched. I no longer have that old active sinful nature which I once had. I now have only a new nature. Yet I must admit that I still have RESIDUAL wretchedness (not much wretchedness but a little of it). Only VESTIGES of wretchedness have survived, otherwise I'm a wonderful person!"