Are the old man and the flesh one and the same? We read the old man has been crucified with Christ, and that we are to mortify the flesh. I'm confused.

How do we distinguish between the flesh and the old man? Generally, they are synonyms. Specifically, the flesh is connected to the body and the old man has to do with the nature of man. Other than that, there is little difference.

THE FLESH

The word, flesh, generally refers to the physical body. But in the Bible, it also has a moral meaning that goes beyond the physical body and deals with the whole range of the earthly thoughts, desires, and feelings. This is the meaning of the lusts of the flesh. In a spiritual sense, "the flesh profiteth nothing" (John 6:63It is the spirit that quickeneth; the flesh profiteth nothing: the words that I speak unto you, they are spirit, and they are life.
See All...). In the flesh are "the motions of sin" (Romans 7:5For when we were in the flesh, the motions of sins, which were by the law, did work in our members to bring forth fruit unto death.
See All...). In our flesh "dwelleth no good thing" (Romans 7:18For I know that in me (that is, in my flesh,) dwelleth no good thing: for to will is present with me; but how to perform that which is good I find not.
See All...).  Our flesh serves "the law of sin" (Romans 7:25I thank God through Jesus Christ our Lord. So then with the mind I myself serve the law of God; but with the flesh the law of sin.
See All...) and in the flesh we cannot please God (Romans 8:8So then they that are in the flesh cannot please God.
See All...). The Christian is to deal with the flesh in the following manner:

1. Refuse to walk after the flesh (Romans 8:1There is therefore now no condemnation to them which are in Christ Jesus, who walk not after the flesh, but after the Spirit.
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2. Do not make provision for the flesh to fulfill the lusts thereof (Romans 13:14But put ye on the Lord Jesus Christ, and make not provision for the flesh, to fulfil the lusts thereof.
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3. Walk in the Spirit so as to not fulfill the lust of the flesh (Galatians 5:16This I say then, Walk in the Spirit, and ye shall not fulfil the lust of the flesh.
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4. Have no confidence in the flesh (Philippians 3:3God came from Teman, and the Holy One from mount Paran. Selah. His glory covered the heavens, and the earth was full of his praise.
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5. Abstain from fleshly lusts (1 Peter 2:11Dearly beloved, I beseech you as strangers and pilgrims, abstain from fleshly lusts, which war against the soul;
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But we are helped in our battle with the flesh by our position in Christ and in the Spirit. Positionally, a believer is not walking in the flesh (though in practice he may do so for a time). In other words, we already have the victory in Christ if we will only practice the victory God has already given us. Therefore, we are "not in the flesh, but in the Spirit" (Romans 8:9But ye are not in the flesh, but in the Spirit, if so be that the Spirit of God dwell in you. Now if any man have not the Spirit of Christ, he is none of his.
See All...). They that belong to Christ have already "crucified the flesh with the affections and lusts" (Galatians 5:24And they that are Christ's have crucified the flesh with the affections and lusts.
See All...). We are already "circumcised with the circumcision made without hands, in putting off the body of the sins of the flesh by the circumcision of Christ" (Colossians 2:11In whom also ye are circumcised with the circumcision made without hands, in putting off the body of the sins of the flesh by the circumcision of Christ:
See All...). This position we have in Christ acts as the ground by which we deny ourselves and live by the power of the Spirit. It is our provision for victory over the flesh.

THE OLD MAN

The "old man" is only used three times in the New Testament (Romans 6:6Knowing this, that our old man is crucified with him, that the body of sin might be destroyed, that henceforth we should not serve sin.
See All...).  The old man could be called the old nature. The old man is desginated as being crucified with Christ (Romans 6:6Knowing this, that our old man is crucified with him, that the body of sin might be destroyed, that henceforth we should not serve sin.
See All...) and put off (Ephesians 4:22-24 [22] That ye put off concerning the former conversation the old man, which is corrupt according to the deceitful lusts; [23] And be renewed in the spirit of your mind; [24] And that ye put on the new man, which after God is created in righteousness and true holiness.
See All...; Colossians 3:9-10 [9] Lie not one to another, seeing that ye have put off the old man with his deeds; [10] And have put on the new man, which is renewed in knowledge after the image of him that created him:
See All...). These passages show the old man to have been put off.  In one sense, the issue is settled. But there is another issue with the old man.

Consider Colossians 3:9-10 [9] Lie not one to another, seeing that ye have put off the old man with his deeds; [10] And have put on the new man, which is renewed in knowledge after the image of him that created him:
See All... - "Lie not one to another, seeing that ye have put off the old man with his deeds; And have put on the new man, which is renewed in knowledge after the image of him that created him." Although the old man has been put off and the new man has been put on, this is not a guarantee of victory over sin. In fact, the believers are here told to use the fact that the old man is put off as a basis for not lying to one another. In other words, the old man was put off, but they still had to be told not to lie to one another. The larger passage in Colossians 3 shows that they had many other sins they needed to put off as well. What is the answer to this perplexity? How could the old man be put off before the sins of the old man were done away with?

It has to do with an important concept in practical sanctification. God gives us the victory positionally before we experience the victory practically. Positionally, the old man has been put off forever. I am in Christ and the old man has been crucified with Him on the cross.  Practically, the old man remains as a force that must be dealt with on a day by day basis. We must trust in God's sufficiency to continually live the life of the new man. God has made us a new man. He has given us a new nature. Though we may have to put off and put on different practices throughout our Christian life, we can rest assured that God has already implanted in us a new man and has cast aside the old man. The Christian life is one of possessing our possessions (see Obadiah 1:17But upon mount Zion shall be deliverance, and there shall be holiness; and the house of Jacob shall possess their possessions.
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