What does Paul mean when he speaks of "in Christ"?

1 Corinthians 12:26

If one part suffers, every part suffers with it; if one part is honored, every part rejoices with it.

From a Word of Faith perspective as believers we experience a spiritual duality of location being both within our bodies and at one with Christ sharing together in an ether which is connected to Heaven and Earth.

1 Corinthians 12:27

Now you are the body of Christ, and each one of you is a part of it.

1 Corinthians 11:3

But I want you to realize that the head of every man is Christ, and the head of the woman is man, and the head of Christ is God.

This place is implicated through our total and complete union with He Who Was, Who Is and Who is to Come. This union grants us a place as a "cell" in the spiritual multicellular organism who is Christ the Almighty God. Unlike natural organisms the vitals of life depend and are drawn solely from the head who is God.

Romans 11:21

For if God did not spare the natural branches, he will not spare you either.

2 Peter 2:1

But there were also false prophets among the people, just as there will be false teachers among you. They will secretly introduce destructive heresies, even denying the sovereign Lord who bought them--bringing swift destruction on themselves.

1 John 2:19

They went out from us, but they did not really belong to us. For if they had belonged to us, they would have remained with us; but their going showed that none of them belonged to us.

Our place within Christ may be severed should we or He choose as such. (Yes not all groups hold as such)

For further exposition please read the following:

POWERFUL PREPOSTIONS

But he that is joined unto the Lord is one spirit. I Corinthians 6:17

The phrase “in Christ” is never translated to mean anything else except “in union with Christ.”

Mark Hankins

In Paul’s epistles, these important prepositions go unnoticed: for, with, in, by, and through. These words help us understand our identification with Christ. They are the connecting words that show the relationship of the subjects mentioned, in this case, the believer’s identification with Christ.

The preposition "for" shows substitution. Christ died “for” us or in our behalf. The preposition with shows identification. The preposition "in" shows union with Christ. The preposition "through" shows application. For example: “I can do all things through Christ who strengtheneth me,” Philippians 4:13.

When you were born again, your spirit was joined to the Master, or joined to Christ. Like a bay of water is one with the ocean, your spirit is one with Christ. When the water rises in the ocean, it rises in the bay. The same stuff that is in Christ right now is in you the same life, the same victory, the same joy, and the same power!

And also a slightly different interpretation:

How Would You Like To ‘Take a Stroll’ In the Spirit Today? Sparkling Gems July 13th

This I say then, Walk in the Spirit, and ye shall not fulfil the lust of the flesh. — Galatians 5:16

How would you like to “walk in the Spirit” every day of your life? Does this proposal sound like an impossibility, or do you think that constantly walking in the Spirit is a possibility you should try to achieve? To answer the question of whether or not it is possible to consistently walk in the Spirit, let’s look at Paul’s words in Galatians 5:16. This verse says, “This I say then, Walk in the Spirit, and ye shall not fulfil the lust of the flesh.”

The word “walk” is the Greek word peripateo. It appears in the New Testament ninety-five times and has a very clear meaning. The word peripateo is a compound of the words peri and pateo. The word peri means around and suggests the idea of something that is encircling. In many cases it means concerning, but in this case it expresses the idea of encircling. The word pateo means to walk. It denotes the movement of the feet, and it can be translated to walk, to step, to stride, to tread, or even to trample. When these two words are compounded into one as they are in Galatians 5:16, it means to habitually walk around in one general vicinity. Thus, this word peripateo was often translated as the word “live.”

This means that instead of being translated “walk in the Spirit,” the phrase in Galatians 5:16 could be translated “live in the Spirit.” This is a good rendering of the word peripateo, for indeed it suggests a person who has walked in one region for so long that it has now become his environment, his place of daily activity, the sphere that encircles his existence. One expositor notes that the word peripateo could be best explained by thinking of a person who has walked one path so habitually that he would be able to walk that path blindfolded because it is his path, his sphere, the place where he has habitually lived and functioned.

My wife and I recently invited a precious elderly couple whom we dearly love to come visit our family. The wife responded, “You see, Rick, I’ve lost most of my eyesight, so it’s best if I stay home. At least at home I know where all the furniture is, so even though I can’t see too well, I can still walk around.”

I was saddened to hear about this dear woman’s failing eyesight, but her words caused me to think of the Greek word peripateo in Galatians 5:16, which pictures a person who has frequented one area so repeatedly that it has become second nature to him. He needs no help to walk there, because he knows that path. It is his path, his walk, his realm of life, and he feels very safe and comfortable there.

In the secular literature of New Testament times, the word peripateo often meant to stroll. In fact, many Greek scholars suggest that the best way to translate Galatians 5:16 is “stroll in the Spirit.” To stroll is to leisurely walk. A person who strolls is not an anxious, frustrated person who is fighting to do something or to get somewhere; rather, he is restful, relaxed, unhurried, peaceful, and calm. This wonderfully describes what it is like to walk in the Spirit. You see, when a person walks in the Spirit, the stress and anxieties of life are removed, and he moves over into a realm where he can stroll along in continual rest, peace, and calmness.

Paul goes on to say that if you walk in the Spirit, “…ye shall not fulfil the lust of the flesh.” The word “lust” is from the Greek word epithumia. The second part of the word is the Greek word thumos, which describes an urge, a longing, a craving, a passion, or something that is excited. The word epi usually means over, but when combined with the word thumos, it means to get extremely excited for or over something. In fact, this excitement is so vigorous that it becomes a fervent passion, almost like an obsession, a mania, or a very strong desire.

In Ephesians 2:3, Paul states that before we came to Jesus Christ, we walked “…in the lusts of our flesh, fulfilling the desires of the flesh….” The word “lusts” is this same word epithumia. The word “desires” is from the Greek word thelema, which denotes one’s will, intention, plan, or desire. In short, it means the flesh has a mind of its own. And if allowed to do so, the flesh will become obsessed with a fleshly temptation, fervently stirred up as it yearns to fulfill its deep, dark desires.

But Galatians 5:16 provides the answer to the flesh. It says if you “…walk in the Spirit, ye shall not fulfil the lust of the flesh.” The word “fulfil” is from the Greek work teleo, which means to fulfill, to complete, or to reach one’s goal. But because of the tense and the strong negative that are used in the Greek phrase, Paul is telling us that if we walk in the Spirit, we have basically pulled the plug on the flesh! As a result, we have nullified the yearnings of the flesh so that they will never be fulfilled.

Because of the various words used in this verse, Galatians 5:16 conveys this idea:

“Make the path of the Spirit the place where you habitually live and walk. Become so comfortable on this spiritual path that you learn to leisurely and peacefully stroll along in that realm. Living your life in this Spirit realm is the best way to guarantee that you will not allow the yearnings of your flesh to creep out and fulfill themselves.”

It is time for you to do everything you can to move up into a higher realm. Fixate on the goal of walking in the Spirit. Develop your own human spirit; do what you can to become more sensitive to the Spirit of God. When you become more spiritually sensitive, it will be easier for you to keep in step with the Holy Spirit. And as you follow Him and live to please the Lord, you will find that walking in the Spirit becomes a habit. You’ll deny your flesh for so long that its voice will eventually become weaker and weaker and weaker — until, finally, it will no longer have any authority in your life.

God is calling you higher! He wants you to leave the low life you’ve been living and to come up to the spiritual path He has destined for you to walk on in your life. In that higher realm, you will experience love, joy, peace, longsuffering, gentleness, goodness, faith, meekness, and temperance. These are the fruit that the Holy Spirit produces! What a contrast to the rotten, decaying garbage that the flesh produces! The Spirit always produces life!

I agree that "in Christ" as interpreted in the Complete Jewish Bible in Romans 8:1 as our being "in union with the Messian Yeshua" (Christ) is true. "Therefore, there is no longer any condemnation awaiting those who are in union with the Messiah Yeshua." Jesus defines our union with Him : John 17:22-23 "And the glory which thou gavest me I have given them; that they may be one, even as we are one:" "I in them, and thou in me, that they may be made perfect in one; and that the world may know that thou hast sent me, and hast loved them, as thou hast loved me."
Jesus further defines our union with Him in: John 15:5 I am the vine, ye are the branches: He that abideth in me, and I in him, the same bringeth forth much fruit: for without me ye can do nothing." God's definition of "fruit" is found in Galatians 5:22-23:" But the fruit of the Spirit is love, joy, peace, longsuffering, gentleness, goodness, faith,""Meekness, temperance: against such there is no law." Since the fruit of the Spirit only grows as we abide in Christ therefore Christ is the source, and is the Fruit of the Spirit. The fruit of the Spirit is not an imitation of Christ nor is it just trying to apply the teachings of Christ: It is Christ as we are in spiritual union with Him by the Power of the Holy Spirit. Christ grows His Divine Nature / Character of God as we are living members of His Spiritual Body. This is not mysticism, but rather it is true Biblical Word spiritual reality in Christ, Who is The Word of Life.
As the Bible says: 1 Peter 2:2-3:"As newborn babes, desire the sincere milk of the word, that ye may grow thereby:"""If so be ye have tasted that the Lord is gracious." Christ is the "sincere milk of the word". Christ said:John 6:48 : "I am that bread of life." Jesus said for us to eat: John 6:50 "This is the bread which cometh down from heaven, that a man may eat thereof, and not die." Colossians 3:4 "When Christ, who is our life, shall appear, then shall ye also appear with him in glory." Our Heavenly Father is glorified as He grows in us by His Son, Jesus, His Divine Nature, The Fruit of the Spirit: John 15:8 "Herein is my Father glorified, that ye bear much fruit; so shall ye be my disciples." No flesh shall glory in God's Presence: 1 Corinthians 1:29-31: "That no flesh should glory in his presence.""But of him are ye in Christ Jesus, who of God is made unto us wisdom, and righteousness, and sanctification, and redemption:""That, according as it is written, He that glorieth, let him glory in the Lord." Colossians 3:11 "Where there is neither Greek nor Jew, circumcision nor uncircumcision, Barbarian, Scythian, bond nor free: but Christ is all, and in all." All Glory has been, and is, and will be only unto Him forever and forever. Amen.

To be in Christ is the safest place we can be. Outside of Christ--in other words, standing in our own merits--is the most dangerous place we can be. Paul tells us in 2 Corinthians

"Therefore if anyone is in Christ, he is a new creature; the old things passed away; behold, new things have come. Now all these things are from God, who reconciled us to Himself through Christ and gave us the ministry of reconciliation, namely, that God was in Christ reconciling the world to Himself . . ." (5:17-19a NASB Updated).

Notice that Paul uses the word in twice.

• if anyone is in Christ

• God was in Christ reconciling the world

The first use of in tells us that our standing, or position, before God is not in our own merits, but in the merits of Christ. In other words, we cling to Him as our agent of salvation. In Christ, we are the righteousness of God (see 2 Corinthians 5:21). Our part is simply to believe; Christ did--and continues to do--what it took to reconcile us to God. Speaking more accurately, this reconciliation is of God to us.

The second in tells us that because of our sin, God had to turn His back to us. The good news is that God in Christ made it possible through Christ's cross-death for God to turn His face toward us. Judicially speaking, God then sees us in Christ. Again, this is the safest and best place in which anyone can be. Furthermore,

"[Christ] . . . is able also to save forever those who draw near to God through Him, since He always lives to make intercession for them" (Hebrews 7:25 Hebrews 7:25 NAS).

There will never come a time, either in this life or the next, when all true believers will not be in Christ. Scripture tells us that in the person of the Holy Spirit, Jesus is and always will be our advocate (Gk. paraklete) before the Father. From the NET Bible at Bible.org:

"This word [paraklete, or paraclete] occurs 5 times in the New Testament, all in the writings of John. Four instances are in the Gospel and one in the First Epistle. In the Gospel the in the Epistle, 1 Jn 2:1. 'Paraclete' is simply the Greek word transferred into English. The translation of the word in English Versions of the Bible is 'Comforter' in the Gospel, and 'Advocate' in the Epistle. The Greek word is parakletos, froth the verb parakaleo. The word for 'Paraclete' is passive in form, and etymologically signifies "called to one's side." The active form of the word is parakletor, not found in the New Testament but found in Septuagint in Job 16:2 in the plural, and means 'comforters,' in the saying of Job regarding the 'miserable comforters' who came to him in his distress.

"In general the word signifies: (1) a legal advocate, or counsel for defense, (2) an intercessor, (3) a helper, generally. The first, or technical, judicial meaning is that which predominates in classical usage, corresponding to our word 'advocate,' 'counsel,' or 'attorney.' The corresponding Latin word is advocatus, 'advocate,' the word applied to Christ in English Versions of the Bible in the translation of the Greek word parakletos, in 1 Jn 2:1. There is some question whether the translation 'Comforter' in the passages of John's Gospel in the King James Version and the Revised Version (British and American) is warranted by the meaning of the word. It is certain that the meaning 'comforter' is not the primary signification, as we have seen. It is very probably, however, a secondary meaning of the word, and some of its cognates clearly convey the idea of comfort in certain connections, both in Septuagint and in the New Testament (Gen 37:35; Zec 1:13; Mt 5:4; 2 Cor 1:3,4). In the passage in 2 Corinthians the word in one form or another is used 5 times and in each means 'comfort.' In none of these instances, however, do we find the noun 'Paraclete,' which we are now considering."

Hebrews 9:24 in the New Living Translation tells us

"For Christ has entered into heaven itself to appear now before God as our Advocate. He did not go into the earthly place of worship, for that was merely a copy of the real Temple in heaven. Nor did he enter heaven to offer himself again and again, like the earthly high priest who enters the Most Holy Place year after year to offer the blood of an animal. If that had been necessary, he would have had to die again and again, ever since the world began. But no! He came once for all time, at the end of the age, to remove the power of sin forever by his sacrificial death for us."

In conclusion, Christ's sacrificial death on our behalf will forever be our defense before a holy and righteous God. Christ, in effect, tells the Father whenever we sin,

"Father, this child of yours is in me. When he confesses his sin and pleads my blood as the basis for his forgiveness, forgive him, for my sake!"

When Satan, the accuser of the brethren (Revelation 12:10) accuses us before God, Christ comes to our defense. He is truly a lawyer in whom we can have full confidence! We will always be safe in His hands.

Since there are tons of different places in which Paul uses the phrase, some specific references might help here.

In Acts 24:24, for example, Paul refers to "faith in Christ Jesus." Faith here refers not to the pseudo-power claimed by the "word of faith" movement, but rather having faith in the testimony of Christ.

Romans 6:3, on the other hand, refers to being "baptized into Christ." Here the Greek word baptizo literally means "immersed" or fully a part of Christ. It could also refer, in this context, to being baptized in the name of Christ.

Romans 8:1 provides another variation of the phrase: "There is now no condemnation for those who are in Christ Jesus." [emphasis mine] Perhaps this is the type of phrase you're looking for, as Paul uses this terminology quite a bit. The Complete Jewish Bible may provide a clarification in its translation: "Therefore, there is no longer any condemnation awaiting those who are in union with the Messiah Yeshua." [emphasis mine] (Yeshua is the commonly accepted Hebrew name translated into Greek and Latin as Iesus, or into English as Jesus.)

Galatians 2:20, while it may not use the phrase in all translations, may further explain the concept. "I have been crucified with Christ, and it is no longer I who live, but Christ lives in me. So the life I now live in the body, I live because of the faithfulness of the Son of God, who loved me and gave himself for me." To Paul his old life as Saul of Tarsus, persecutor of Christians, was gone. Saul was dead, crucified as Christ was. His new life through a full-bonded union with Christ was represented by his new name, Paul the apostle. His life was completely subsumed by the lift of Christ. Obviously, as @Narnian points out, this is not a physical movement into a place or person, but a metaphysical or spiritual replacement.