Many seem to be confused about this biblical term, but what the word represents is the "natural" man, born unto this world. (as the Lord said) For that which is born of the flesh "is Flesh". Now religion has attempted to confuse this by some doctrines that promote a false understanding of the term? Many would claim there is a good part of the natural man (acceptable to God) and then a "sinful nature" in natural man. This is a complete error. "NOTHING GOOD LIVES IN THE FLESH" Until a believer becomes as Paul described as one who has "NO CONFIDENCE IN THE FLESH" and only trust in the Spirit of God, working righteousness through faith and love from the spirit, that believer is what the scriptures call "carnal". They are not "spiritual". For those who are "spiritual" are not looking and judging things according to the flesh, but according to the spirit. This is a mystery and the "mystery of godliness" but one MUST ACCEPT THE CROSS OF CHRIST, AS ONES OWN DEATH, to enter into true Godliness and true holiness.
The flesh is the physical body. The word has the same meaning in the Old Testament and in the New Testament. Our nature, in fact, is flesh and blood. This is as opposed to spirit. God is spirit. We are flesh and blood. That is our nature. Christ partook of our nature. Hebrews 2:14 Since therefore the children share in flesh and blood, he himself likewise partook of the same nature
Why is this so confusing? God sent the flood to make an end of all flesh, everything he had made, because the earth was filled with violence through them. God said he would destroy them, meaning all flesh, everything with the breath of life in it. Gen. 6:17
I'm not going to get into this sinful nature business because Jesus said man is evil and no one is good but God alone. I'm just telling you what the word flesh means.
The flesh is the physical body. The physical body has physical desires like sex, money, food, clothing, etc. This is a weakness the devil exploits. It is a weakness of the physical body, our nature being flesh and blood. It's because we are flesh and blood in nature, that we are weak. I told you about endorphines. The devil exploits this weakness and leads us away from God and the teachings of our Master, Jesus Christ, to acquire things, even to ask God for money. Note, having money, you get a feeling of well being, security, etc. Jesus said, do not be anxious about your life, what you shall eat or what you shall drink, nor about your body, what you shall put on. The mind that is set on the flesh is set on what you will wear, what you will eat.
Paul bemoans this weakness re. coveting. He doesn't want to, but how can you prevent it? He sees a law at work in his members, his flesh, to covet, even though he knows it is a sin. The flesh has physical desires. The desire of the flesh is well being. Romans 7:15 'I do not understand my own actions. For I do not do what I want, but I do the very thing I hate.' So he sees this warfare going on between the law of God in his inmost self and the law of sin in his flesh. 'Wretched man', he says, 'Who will deliver me from this body of death?' Ro. 7:24