The question being answered in this reply is "What does it mean to be in Christ"?. 

I have found the phrase “in Christ” in 77 verses of the KJV bible.  Acts 24:24, Rom:24, 3 in rom 8, 9:1, 15:5, 4 in Rom 16, 1cor 1:30, 3:1, 4:10, 15, 17; 15:19, 22, 31, 16:24. 10 in 2nd cor, 6 in Gal; 11 in Eph; 7 in Phil; 4 Col; 2 Thes; 3 1st Tim; 7 in 2nd Tim; 3 in Phm; 1 Pet 3:16, 5:14   

To understand its use comprehensively it may mean reading each use in context, which may mean reading the whole epistle.  Something I do not presently have the time to do.  I think your question is leaning towards the associated questions.  Are believers presently in Christ, can they lose that position, do they have to keep the laws of God?

I will mainly answer the last one as whether or not they are “in Christ” would depend on whether they have to keep the laws. If they do not then there is a possibility they may be in Christ.  If they do have to keep them and are not, then the likelihood is they are not “in Christ”.  This will also address the second question as to whether they can lose that position.  If they have to keep the laws, did keep them at one time; but then fell away (stop keeping them) then they may have lost a former “in Christ” position. 

A major point in understanding the writers use of “in Christ” is to whom they were writing, what were those readers doing and not doing and what were they being requested to do or not do?  I think this is where Christians fall short in their understanding of scripture and such concepts of “in Christ”.  They were and still are, in my mind, only two groups in God’s eyes.  Those He calls my people and the rest.  Those in Christ and those not, those who will be saved and those not.  The division between these two groups are those who obey the Father’s will and those who do not.  The Father’s will and His division is clear in what we call the O.Testament.  It was the obedient Israelites plus strangers (gentiles) who attached themselves to the group as the mixed multitude who came out of Egypt (Ex 12:38).  This group had to keep the laws of God and were punished for not keeping it (Ex 15:33) as well as not having faith  (see account of Caleb and Joshua in Num 13 & 14). This criteria continued in other writings of the O.T. as Jonah.  It is when we come to the N. Testament that Christians use faith, grace, Christ as an excuse.  However, scripture is clear on that neither of these excuses the believer or one desiring to be saved from keeping the law (See the “God Forbid” scriptures attached). 

Now let us turn to the specific 77 scriptures mentioned.  Clearly from the God forbid scriptures, these “in Christ” ones cannot be saying one does not have to keep the law especially when we read in Rev 12:17, 14:12 and 22:14 it is those that keep the commandments of God and have the faith of Christ that get the reward.  Infact Rev 22:14 goes further, it saves those who keep the commandments “..have right to the tree of life, and may enter in through the gates..”.  In other words, they cannot be denied entry!  Compared to those who think they have a right due to their standard or understanding of good works etc, yet are denied entry

Mat 7:21  Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven. Mat 7:22  Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works? Mat 7:23  And then will I profess unto them, I never knew you: depart from me, ye that work iniquity.  

1. To whom were writers writing: Either believing Jews (Messianic), or Gentiles wishing to be part of that group (grafted in).  See Article Acts 11 -1 9.  In other words these were persons who kept the law; but some Jews claimed the Gentiles should also be circumcised.  i.e.  Act 15:1  And certain men which came down from Judaea taught the brethren, and said, Except ye be circumcised after the manner of Moses, ye cannot be saved. Act 15:2  When therefore Paul and Barnabas had no small dissension and disputation with them, they determined that Paul and Barnabas, and certain other of them, should go up to Jerusalem unto the apostles and elders about this question.  Act 15:6  And the apostles and elders came together for to consider of this matter.  

Act 24:24  … and heard him concerning the faith in Christ.   Jews hearing about Pauls faith in Christ as the saviour / promised messiah.  See also v5, 14-15, 18, 27 that context is among Jews. 

To see if epistle of Romans is saying one does not have to keep law, read article “Romans In Perspective” a list of Romans scriptures show that is not the case.  The law is to be kept.  Withot the law there wold be no need for a saviour from the consequences or breaking any.  God is not a respector of persons, the criteria is obedience Gal 3:28  There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus. 

2. What was being taught: 1Co 1:23  But we preach Christ crucified, unto the Jews a stumblingblock, and unto the Greeks foolishness; 1Co 1:24  But unto them which are called, both Jews and Greeks, Christ the power of God, and the wisdom of God. 1Co 2:2  For I determined not to know anything among you, save Jesus Christ, and him crucified. 1Co 4:17  For this cause have I sent unto you Timotheus, who is my beloved son, and faithful in the Lord, who shall bring you into remembrance of my ways which be in Christ, as I teach every where in every church.

We must also here remember what guidance Paul told Timothy to get an understanding of what Paul was teaching and from where his teachings came 1Ti 1:9  Knowing this, that the law is not made for a righteous man, but for the lawless and disobedient, for the ungodly and for sinners, for unholy and profane, for murderers of fathers and murderers of mothers, for manslayers, 1Ti 1:10  For whoremongers, for them that defile themselves with mankind, for menstealers, for liars, for perjured persons, and if there be any other thing that is contrary to sound doctrine;

2Ti 2:15  Study to shew thyself approved unto God, a workman that needeth not to be ashamed, rightly dividing the word of truth. (that study coming from) 2Ti 3:15  And that from a child thou hast known the holy scriptures, which are able to make thee wise unto salvation through faith which is in Christ Jesus. 2Ti 3:16  All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: (The ALL scripture only referring to the O. Testament as that was all that was available; no N. Testament).  Paul directed Timothy to the same source he was using to be a teacher of the Gentiles  2Ti 1:11  Whereunto I am appointed a preacher, and an apostle, and a teacher of the Gentiles.

Conclusion:

When asked how to get eternal life in Mat 19:16, Mar 10:17; Luke 10:25, 18:18 Jesus replied keep the commandments as written in the law (Mat 19:16; Luk 10:25).  He also said the scriptures testify of him.  The scriptures are about the law and if studied one should see they are the spoken of similar to Jesus (truth, light, means of being saved, etc (Joh 5:39  Search the scriptures; for in them ye think ye have eternal life: and they are they which testify of me).    

In the new Testament the same question is asked Act 16:30  And brought them out, and said, Sirs, what must I do to be saved? Act 16:31  And they said, Believe on the Lord Jesus Christ, and thou shalt be saved, and thy house. The reply of believing in the Messiah, must coincide with what the Messiah himself said.  Pointing to belief in the Messiah being keeping the commandments as written in the law (too much to explain here). 

Later we read the apostle Paul saying 1Ti 2:4  Who will have all men to be saved, and to come unto the knowledge of the truth. Remember Paul told Timothy to teach from the scriptures which he had known from a child, the O. Testament. 

Galatians:  If we read the whole of Galatians in context, with reference to Abraham, his calling and promise given to him before the circumcision covenant we should see its topic is circumcision.  That is the part of the law Paul is reasoning Gal 3:28  There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus.  Gal 6:15  For in Christ Jesus neither circumcision availeth any thing, nor uncircumcision, but a new creature.

For example see the mention of circumcision throughout the epistle i.e. Gal 2:3, 7-9, 12; 5:2-6, 11 and right to the end in 6:12-15. 

Ephisians:  Eph 2:1  And you hath he quickened, who were dead in trespasses and sins;

Eph 2:2  Wherein in time past ye walked according to the course of this world, according to the prince of the power of the air, the spirit that now worketh in the children of disobedience:

Eph 2:3  Among whom also we all had our conversation in times past in the lusts of our flesh, fulfilling the desires of the flesh and of the mind; and were by nature the children of wrath, even as others. 

Note persons sinned which is disobedience to keeping the law (1Jo 3:4  Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law).

Eph 2:10  For we are his workmanship, created in Christ Jesus unto good works, which God hath before ordained that we should walk in them.  Eph 2:12  That at that time ye were without Christ, being aliens from the commonwealth of Israel, and strangers from the covenants of promise, having no hope, and without God in the world: Eph 2:13  But now in Christ Jesus ye who sometimes were far off are made nigh by the blood of Christ. Eph 2:19  Now therefore ye are no more strangers and foreigners, but fellow citizens with the saints, and of the household of God; Eph 2:20  And are built upon the foundation of the apostles and prophets, Jesus Christ (Yahshua) himself being the chief corner stone; 

Eph 3:6  That the Gentiles should be fellow heirs, and of the same body, and partakers of his promise in Christ by the gospel:

We ought to remember Abraham was a law keeper even before it was passed onto to his descendants through Moses.  See Gen 15:10 how he did not divide the birds to be sacrificed as in Lev 1:17; Jacob his son knew about requirements for a sacrifice in Gen 22:7.  Gen 17:1  The LORD appeared to Abram, and said unto him, I am the Almighty God; walk before me, and be thou perfect. Gen 17:2  And I will make my covenant between me and thee, and will multiply thee exceedingly. 

The promise spoken of in Ephesians is derived from Gen 22:18  And in thy seed shall all the nations of the earth be blessed; because thou hast obeyed my voice. This is what Abraham obeyed Gen 26:4  … and in thy seed shall all the nations of the earth be blessed; Gen 26:5  Because that Abraham obeyed my voice, and kept my charge, my commandments, my statutes, and my laws. 

Phi 3:9  And be found in him, not having mine own righteousness, which is of the law, but that which is through the faith of Christ, the righteousness which is of God by faith: Eph 2:8  For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: 

We go through the doorway of faith to get the grace of God.  Most people end the sentence at “by grace are ye saved” and cut off the “through faith”.  Prior to the coming of the Messiah we obeyed the laws of God through Moses either as an Israelite or a grafted in stranger.  We tried to become a new person living as god prescribed.  We got our forgiveness for transgressions of his instructions through the annual sacrifice of the High priest, say Aaron.  At the coming of the Messiah we got the same law as did Moses; but at the resurrection of the Messiah, who is the actual High priest we get the same forgiveness for sin transgression only this time through the Highest priest and His blood sacrifice rather than of rams and goats.  We are still called to live under those righteous instructions rather than of the world’s. 2Co 5:17  Therefore if any man be in Christ, he is a new creature: old things are passed away; behold, all things are become new.  He did not come to take away the necessity to keep the law only administer a better sacrifice if we acknowledge our sin and repent.  That is to be in Christ, when we are in His and His father’s system.  2014