WHAT DOES IT MEAN " TO BE IN CHRIST " ?
My favorite question when dealing with any Scripture: "What does it mean?" Don't just memorize it. Be able to explain it.
Since you're looking at statistics, I searched The New Testament in the Original Greek, Byzantine Text Form, 2005, by Robinson and Pierpont. The wording "ev" + the dative form of "Christos" is used 77 times. 3x in 1 Peter, 1x in Revelation, the rest are in Paul's writings. This Greek wording is the most literal for "in Christ". If I go to an English translation, the NKJ shows 87 instances of "in Christ" in the NT. So, there will be other Greek prepositions or wording in use and possibly some nuances in meaning to be looked at. IOW, if I'm translating, I attempt to be as literal as possible, even if it doesn't always make simple sense in English, so I can read English and be aware of differences in the Greek.
I'd begin by looking at the lexical meaning of "en" which is mostly translated as "in" but as with most Greek words, there is more than this simplicity.
Firstly, one way to look at Greek prepositions is spatially. If we draw a circle, so we have the inside and outside of this circle, en is being inside of it. The other prepositions say something different. For example, eis most simply means "into" and we would draw a line from outside to inside to show the movement from out to in. Interestingly, when John says "believe in Christ" he typically uses "eis" which looking simply and spatially would show a transition from unbelief to belief - from being outside to inside (en). This spatial concept can begin to inform us what it means to be "in Christ".
From there I'd go to the Greek Lexicons to see what this word en can mean. This will be lengthy, but the possible meanings for this simple preposition per BAGD Greek Lexicon are shown below, Due to posting limitations I'm going to paste just the headings:
You'll find in this instance this Lexicon will explain what "in Christ" means. Personally, and it's not just me, but I don't rely on Lexicons to make doctrinal conclusions. Some of them can have a theological bias that will reveal itself. The translator or interpreter need to determine from language, grammar, context, historical culture, and analyzing all the ways God uses the word in Scripture, what the word and phrase means. We see from the Lexicon that even if we translate this word as "in" there will be different nuances as to what "in" means. Many times, the writer may use some form of grammar or structure like parallelism to help define a word or phrase. Also, in the Bible, other teachings covering the topic may add information to refine the meaning. So, the translator or interpreter will need to pick these things up and refine the lexical definition to incorporate it and bring out the actual meaning. Even if one does not know Greek, I'd bet the spatial concept and choosing from the Lexical information below can provide information that begins to provide meaning to the phrase "in Christ".
ἐν preposition from ἐν
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Bauer-Danker, Greek-English Lexicon of the NT (BDAG)
[BDAG] ἐν
• ἐν prep. w. dat. (Hom.+). For lit. s. ἀνά and εἰς, beg. For special NT uses s. AOepke, TW II 534-39. The uses of this prep. are so many and various, and oft. so easily confused, that a strictly systematic treatment is impossible. It must suffice to list the main categories, which will help establish the usage in individual cases. The earliest auditors/readers, not being inconvenienced by grammatical and lexical debates, would readily absorb the context and experience little difficulty.
1. marker of a position defined as being in a location, in, among (the basic idea, Rob. 586f)
a. of the space or place within which someth. is found, in:
b. on ἐν τῷ ὄρει (X., An. 4, 3, 31; Diod. S. 14, 16, 2 λόφος ἐν ᾧ=a hill on which; Jos., Ant. 12, 259; Just., D. 67, 9 ἐν ὄρει Χωρήβ) J 4:20f; Hb 8:5 (Ex 25:40). ἐν τῇ ἀγορᾷ in the market Mt 20:3. ἐν τῇ ὁδῷ on the way Mt 5:25. ἐν πλαξίν on tablets 2 Cor 3:3. ἐν ταῖς γωνίαις τῶν πλατειῶν on the street corners Mt 6:5.
c. within the range of, at, near
d. among, in
e. before, in the presence of, etc.
f. esp. to describe certain processes, inward:
2. marker of a state or condition, in
a. of being clothed and metaphors assoc. with such condition in, with
b. of other states and conditions
3. marker of extension toward a goal that is understood to be within an area or condition, into: ἐν is somet. used w. verbs of motion where εἰς would normally be expected wers to the question ‘whither’ (B-D-F §215, 3) Mt 10:16; Lk 10:3; 8:7.
4. marker of close association within a limit, in
a. fig., of pers., to indicate the state of being filled w. or gripped by someth.: in someone=in one’s innermost being
b. of the whole, w. which the parts are closely joined:
c. esp. in Paul. or Joh. usage, to designate a close personal relation in which the referent of the ἐν-term is viewed as the controlling influence: under the control of, under the influence of, in close association with
5. marker introducing means or instrument, with, a construction that begins w. Homer
a. it can serve to introduce persons or things that accompany someone to secure an objective: ‘along with’
α. pers., esp. of a military force, w. blending of associative (s. 4) and instrumental idea
β. impers. (oft. LXX; PTebt 41, 5 [c. 119 BC]; 16, 14 [114 BC]; 45, 17 al., where people rush into the village or the house
b. it can serve to express means or instrumentality in terms of location for a specific action
6.marker of agency: with the help of
7. marker of circumstance or condition under which someth. takes place:
8. marker denoting the object to which someth. happens or in which someth. shows itself, or by which someth. is recognized, to, by, in connection with:
9. marker of cause or reason, because of, on account of
a. gener. ἁγιάζεσθαι ἔν τινι Hb 10:10; 1 Cor 7:14. ἐν τ. ἐπιθυμίαις τῶν καρδιῶν Ro 1:24; perh. ἐν Ἰσαὰκ κληθήσεταί σοι σπέρμα 9:7; Hb 11:18 (both Gen 21:12). ἐν τῇ πολυλογίᾳ αὐτῶν because of their many words Mt 6:7. ἐν τούτῳ πιστεύομεν this is the reason why we believe J 16:30; cp. Ac 24:16; 1 Cor 4:4 (Just., D. 68, 7 οὐχὶ καὶ ἐν τούτῳ δυσωπήσω ὑμᾶς μὴ πείθεσθαι τοῖς διδασκάλοις ὑμῶν=‘surely you will be convinced by this [argument] to lose confidence in your teachers, won’t you?’); perh. 2 Cor 5:2. Sim., of the occasion: ἔφυγεν ἐν τῷ λόγῳ τούτῳ at this statement Ac 7:29; cp. 8:6. W. attraction ἐν ᾧ = ἐν τούτῳ ὅτι for the reason that = because Ro 8:3; Hb 2:18; 6:17.
b. w. verbs that express feeling or emotion, to denote that toward which the feeling is directed;
10.marker of a period of time, in, while, when
a. indicating an occurrence or action within which, at a certain point, someth. occurs
b. point of time when someth. occurs
c. to introduce an activity whose time is given when, while, during
11. marker denoting kind and manner, esp. functioning as an auxiliary in periphrasis for adverbs
12. marker of specification or substance: