Growing
Flesh
In plain words
In the Bible, "the flesh" often means the part of us that wants to live without God.
When Paul talks about "the flesh", he usually does not mean your skin and muscles. He means the old self-centred pull inside you that wants its own way and does not want God in charge. Some Bibles translate it as sinful nature. Everyone has it, Christians included, and everyone knows how it feels.
This is important: the Bible does not say your body is bad. God made bodies and called them good. Jesus Himself "became flesh" (John 1:14). Your body is not the enemy. The problem is a heart turned in on itself.
Go further Growing
Paul says the flesh and the Spirit want opposite things (Galatians 5:16-17). That is why you can feel torn. The answer is not to hate your body or yourself, but this: "walk by the Spirit, and you will not gratify the desires of the flesh" (Galatians 5:16). Those who belong to Christ have "crucified the flesh with its passions and desires" (Galatians 5:24), so don't feed it. Make no provision for it (Romans 13:14), which means not leaving doors open.
A common misunderstanding is that Christians should feel nothing but holy desires. You will still feel the old pull, but it no longer rules you. "The mind of the flesh is death, but the mind of the Spirit is life and peace" (Romans 8:6). Paul could only speak to believers who stayed jealous and quarrelsome "as infants in Christ", and gave them milk (1 Corinthians 3:1-3). Practically: fill your time and mind with good things, not only fight bad ones.
Go deeper Going deeper
The Greek sarx has a range of meanings: physical body, human nature, human weakness, and in Paul often humanity in rebellion against God. Context decides. Paul contrasts flesh with Spirit, two ways of existing, not body against soul. This is a Hebrew way of thinking, not the idea found in some Greek philosophy that matter is evil.
Early Christians fought the teaching that the body is worthless, insisting on Jesus' real body and the resurrection of the body. Christians differ on how much the flesh still shapes a believer's inner life, but agree that in Christ its rule is broken and the body will be raised and made new.
My verses
So I say, walk by the Spirit, and you will not gratify the desires of the flesh. For the flesh craves what is contrary to the Spirit, and the Spirit what is contrary to the flesh. They are opposed to each other, so that you do not do what you want.
Those who live according to the flesh set their minds on the things of the flesh; but those who live according to the Spirit set their minds on the things of the Spirit. The mind of the flesh is death, but the mind of the Spirit is life and peace.
The Word became flesh and made His dwelling among us. We have seen His glory, the glory of the one and only Son from the Father, full of grace and truth.
Instead, clothe yourselves with the Lord Jesus Christ, and make no provision for the desires of the flesh.