From a biblical perspective, the flesh is "that which is contrary to the spirit" (see Galatians 5:17). The flesh and the Spirit are two opposing forces that exist within a believer. The Spirit is just that—the Holy Spirit. The flesh is the part of a believer that disagrees with the Spirit. The makeup of a believer is different from that of an unbeliever, in that an unbeliever does not have the Spirit of God indwelling them. In the case of an unbeliever, the flesh is in agreement with the spirit of that unbeliever. Paul says "our old self was crucified with him in order that the body of sin might be brought to nothing, so that we would no longer be enslaved to sin" (Romans 6:6). What Paul is describing when he says "the body of sin" is the flesh.
What does the Bible mean when it talks about the flesh?
When a believer's old self, sometimes called the "old man," is crucified—by this Paul means brought to faith in Christ, in His redemptive work on the cross—the Spirit indwells the believer, and a "new man" is created. A "new self" with a new nature (2 Corinthians 5:17). This new nature, or new man, is now in conflict with the flesh, because the new man is on the side of the Spirit. Paul famously describes this conflict in Romans, chapter 7, saying "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" (Romans 7:15-18). Later, he says "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!" (v. 22-25). Again he mentions here the "body of death" by which he means the flesh.
The flesh exists in the body, and also in the brain—our neural pathways are affected by the flesh. That is why it is so difficult, oftentimes, for believers to break old habits and patterns of sin. We live for years building habits in the flesh that agree with the "old man" and then when the "new man" arrives, in agreement with the Spirit, we are suddenly in conflict. Some of these habits submit to the Spirit immediately and others are stubborn. One of the most difficult habits to break is one that Paul addresses repeatedly in his letters: the tendency of the flesh to attempt to gain heaven by Law. In Paul's letter to the Galatians, he reminds them that "a person is not justified by works of the law but through faith in Jesus Christ" and again that we have been "crucified with Christ" (Galatians 2:16, 20). He says, "I do not nullify the grace of God, for if righteousness were through the law, then Christ died for no purpose" (Galatians 2:21)
This is confusing because of the many laws and rules that the Bible presents. From the Law of Moses to Jesus' Sermon on the Mount, we see the standard of perfection that God requires. The flesh responds by saying "I can do that" and attempting to obey, despite the obvious fact that none of us can achieve perfection. But the flesh is deceptive. Of the Pharisees, Jesus said "in vain do they worship me, teaching as doctrines the commandments of men" (Mark 7:7). Why did the Pharisees invent new laws? Didn't they have enough to contend with following the Law? They had too much to contend with, and they knew it! So, they created alternate laws that they were able to follow. This is the work of the flesh.
One of the biggest criticisms the Christian church receives from unbelievers is that of hypocrisy. This hypocrisy is real, and the unbelievers are right to criticize us. Like the Galatians, we are deserting the grace of Christ and turning to another gospel (Galatians 1:6). Deceived by the flesh, we try to be good, moral, friendly, nice, loving, faithful people, but we forget that the law was not made to save us—it was designed to aggravate the flesh and show us our imperfections so that we will turn to Christ (Galatians 3:23-25). Because we forget this crucial doctrine, we wind up in a desperate struggle between the flesh and the new man, covering our sins with a thin veneer of morality that the world recognizes as hypocrisy.
We need to take John's advice and come into the light, admitting sin, holding fast to God's forgiveness and Christ's substitutionary righteousness, so that we can be freed to live according to the Spirit (1 John 1:7-9). When the Spirit is in the lead, the flesh takes a backseat and we have peace (Romans 8:5-6). But none of that can be accomplished unless we first admit that we cannot obey the Law in our own strength. We uphold the Law as perfect, and a representation of God's nature, and we strive to walk in His footsteps because when we do, we have peace (Romans 6:6). But, we still must accept two things: obedience to the Law will not get us into heaven, and disobedience to the Law will not exclude us from heaven. There are sins that will destroy your relationships with others, and sins that will destroy your body. There are sins that will wreak havoc on your career and land you in jail. And, once you are in Christ, there are sins that will rob you of sleep, of peace, of joy. But when you are in Christ there is no sin that you can commit that will make God let go of you (Romans 8:1-4). "For I am sure that neither death nor life, nor angels nor rulers, nor things present nor things to come, nor powers, nor height nor depth, nor anything else in all creation, will be able to separate us from the love of God in Christ Jesus our Lord" (Romans 8:38).
What is human nature?
Do we have a body, soul, and spirit? Are we made of two parts or three? Dichotomy or trichotomy?
What is the human soul, according to the Bible?
What is the difference between the soul and the spirit?
What is the heart, according to the Bible?
Truth about Humanity