One of the problems with this debate is how we define our “nature.” It is obvious through Scripture and by looking at ourselves that there is a war going on within a Christian. Some call this the sinful nature warring against the Spirit in us, some call this the indwelling sin that remains in us warring with the Spirit in us, and some call this our flesh warring with our Spirit.
The argument is that at the point of conversion we become a new creation (2 Corinthians 5:17) and therefore our old sinful nature is gone. In one sense this is correct because we do become a new creation and we have new desires. Before, we loved sin and were a slave to sin and now the Christian hates sin and is a slave to Christ. But in another sense this is wrong depending on how we define terms. Even though we are a new creation spiritually, we still have indwelling sin in us (Romans 7:20). We are not condemned for this sin because there is no condemnation for those who are in Christ Jesus (Romans 8:1) but we war against it (1 Peter 2:11)
John MacArthur explains it like this:
So, I am a new creation. I am unfortunately incarcerated in this unredeemed flesh—not just the physical, but all the things that go along with the flesh and my mind and my emotions and my feelings. We still have a sin principle operative.
John MacArthur (2005 Shepherds Conference)
So depending on the terms we use to describe this war (sinful nature, incarcerated flesh, flesh) will determine your position on this subject.
It is so important to understand that you have something in you that is sinful. Whether you call it your sinful nature or as the Bible calls it the “flesh”, we are warring against something in us and it is not only the devil but sin in us. (Romans 7:20).
The Bible is very clear about this war against our sinful flesh even though we are a new creation in Christ.
11Beloved, I urge you as sojourners and exiles to abstain from the passions of the flesh, which wage war against your soul. 1 Peter 2:11
Peter is saying that we have passions in our flesh which we are warring against. Remember that Peter is writing to Christians and not unbelievers.
We see Paul exhorting the Galatians, who are a new creation in Christ, to walk according to the Spirit that is in them and not in the sinful desires of their flesh.
But I say, walk by the Spirit, and you will not gratify the desires of the flesh. For the desires of the flesh are against the Spirit, and the desires of the Spirit are against the flesh, for these are opposed to each other, to keep you from doing the things you want to do. But if you are led by the Spirit, you are not under the law. Galatians 5:16-18
By nature, our Spirit is opposed to our fleshly desires. Flesh is referring to our corrupt nature.
Again, because of the natural war within Christians between our Spirit and flesh (corrupt nature), Paul exhorts the Colossian Christians to put away all of their earthly, sinful desires that they walked in when they were lost but our still struggling with, and walk in their new self that they received when the Holy Spirit entered them at conversion.
Put to death therefore what is earthly in you: sexual immorality, impurity, passion, evil desire, and covetousness, which is idolatry. On account of these the wrath of God is coming. In these you too once walked, when you were living in them. But now you must put them all away: anger, wrath, malice, slander, and obscene talk from your mouth. Do not lie to one another, seeing that you have put off the old self with its practices and have put on the new self, which is being renewed in knowledge after the image of its creator.
Our fleshy desires are still there when we are converted but we now can war against them instead of being a slave to them. This is the sanctification process. Sanctification is when we are conformed to the image of Christ and are enabled more and more to die to our sinful desires and live for righteousness.
R.C. Sproul explains this sanctification:
When we are regenerated by the Holy Spirit and become new creatures in Christ, the power of our fallen nature (flesh) is conquered but not destroyed. Because sanctification is a lifelong process, Christians are daily engaged in warfare with their old nature as they seek to grow in the Spirit and in grace. The old person dies daily as the new person in Christ is strengthened by the indwelling Holy Spirit. The Spirit, who is given to us as a pledge and by whom we are sealed, will prevail in this warfare in the end. In the meantime, however, the struggle can be intense. Christians continue to struggle with sin and temptation. Conversion liberates us from the total control of the flesh, but it does not perfect us. The struggle between the old person (the flesh) and the Spirit continues until we die. After death we are glorified: the flesh is completely put to death, and the new person is completely purified. (Essential truths of the Christian faith, RC Sproul)
Another clear example of this war between our Spirit and flesh is from Paul’s own struggles. We read of them in Romans 7:13-25. Here Paul, now a Christian filled with the Holy Spirit and a new creation, explains his inward war against his Spirit and flesh.
Interpreting Romans 7:13-25
Did that which is good, then, bring death to me? By no means! It was sin, producing death in me through what is good, in order that sin might be shown to be sin, and through the commandment might become sinful beyond measure. For we know that the law is spiritual, but I am of the flesh, sold under sin. For I do not understand my own actions. For I do not do what I want, but I do the very thing I hate. Now if I do what I do not want, I agree with the law, that it is good. So now it is no longer I who do it, but sin that dwells within me. For I know that nothing good dwells in me, that is, in my flesh. For I have the desire to do what is right, but not the ability to carry it out. For I do not do the good I want, but the evil I do not want is what I keep on doing. Now if I do what I do not want, it is no longer I who do it, but sin that dwells within me.
So I find it to be a law that when I want to do right, evil lies close at hand. For I delight in the law of God, in my inner being, but I see in my members another law waging war against the law of my mind and making me captive to the law of sin that dwells in my members. Wretched man that I am! Who will deliver me from this body of death? Thanks be to God through Jesus Christ our Lord! So then, I myself serve the law of God with my mind, but with my flesh I serve the law of sin.
It is important to understand how we interpret Scripture. We us the grammatical-historical interpretation of Scripture.
Here are the reason why Paul is talking about himself as a Christian and talking about a believers struggle with his sinful flesh.
1. When we look at the grammar in this passage we see that Paul is using the present tense, not the past. Paul is not speaking of what he used to be like but what his like now. That is why he says, “Wretched man that I am” and not “Wretched man that I was.”
2. In verse 21 we see that Paul wants to do right where as an unbeliever would not have an intense desire to keep God’s law.
3. The distinction between “I” and the “flesh” in verse 18.
4. His delight in God’s law in verse 22.
5. The fact that Christians are already accounted as righteous in Christ but are yet perfected until the day of redemption. This is shown in the concluding statement of Paul in verse 25 when he says, “I myself serve the law of God with my mind, but with my flesh I serve the law of sin.
This is MacArthur’s take on this passage:
So, in Romans 7, Paul says—and making, I think, a clear distinction: “Sin, it is in me.” But he said, “It’s not I; it is sin that is in me.” So, he understands that he is a new creation. There is a new ego, there is a new “I” and its longings are holy and its affections are spiritual and its love is towards God and its longings are directed in the path of righteousness. Its disposition or its bent is toward the law of God, which he “loves,” he says. But he sees something inside of him warring. So the way I express it there is that we are a new person, a new creation, created in Christ Jesus, with all new longings and desires and loves and affections, but we are incarcerated in this unredeemed humanness. And that’s why in Romans 8, he says, “We are waiting for the redemption of the body.”
Whether you define us as having two natures or one, all biblical Christians should agree that our nature needs continual renewing (Colossians 3:10). This renewing, of course, is a lifetime process for the Christian. Even though the battle for sin is constant, we are no longer under the control of sin (Romans 6:6). The believer is truly a "new creation" in Christ (2 Corinthians 5:17), and it is Christ who will ultimately “rescue [us] from this body of death. Thanks be to God—through Jesus Christ our Lord! (Romans 7:24-25).
The issue is mostly blown out of proportion because we define terms wrongly. On the other hand it is important to see that when you sin as a Christian it is still a sin, a wretched sin. All sin against God is wretched. There is no light sin against the Holy God. Even though, as Christians, we are not condemned for our sin, we still do sin and when we sin it is wretched. The logic goes like this:
If you rape then you are a rapist
If you murder then you are a murderer
If you lie then you are a liar
If you sin then you are a sinner
If all sin is wretched and all who sin are sinners then if you sin wretchedly then you are a wretched sinner.
This logic holds even if you are a Christian because Christians sin. The difference between a Christian sinning and an unbeliever sinning is that Christians hate sin and are grieved by it and repent of it as soon as they fall into it. Even though we are accounted as righteous through Christ, we are still a sinner in the same way as a murder that pays his fine is accounted as a free man, he is still a murder.
So as a Christian we are a wretched sinner that is repenting of our sins, daily, and is conforming to the image of Christ, daily, in this life-long process of sanctification. We should be sinning less as time goes on and we should be more grieved by our sin as time goes on.
Sin is much more than outward actions but is also our thought life, motivations, pride, not loving God like He deserves (which no one has ever accomplished), not loving your husband or wife perfectly, not being a biblical example to your kids and the list goes on.
In this issue it is important to understand the all parties agree that:
1. Christians still struggle with sin through their whole lives (Galatians 5:17, 1John 1:8-9).
2. Christians can and should grow in sanctification throughout their lives by the power of the Holy Spirit dwelling within them.
3. Although Christians are free from the condemnation of the law, sin nonetheless continues to dwell within, and all genuine Christians should be profoundly aware of how far they fall short of God’s absolute standard of righteousness. That is why Paul cries out, “Wretched man that I am! Who will deliver me from this body of death?” (Romans 7:24)
4. Christians are delivered daily from the indwelling power of sin by:
a. walking not according to the flesh but according to the Spirit (Romans 8:4)
b. by not setting their minds on the things of the flesh, but on the things of the Spirit (Romans 8:5)
c. by the indwelling presence of the Spirit of God who dwells in us. (Romans 8:9, 11)