The expression in Christ (and its equivalents in Jesus, in the Lord, in the Son, etc.) occurs 174 times in the New Testament. While it does not occur in any of the Gospels, Hebrews or James, it occurs 21 times in the first two chapters of Ephesians and 10 times in chapter 16 of Romans.
The interesting thing about this seemingly simple expression is the wide range of meaning it conveys in various contexts. In Dr. Clarence Hale’s booklet entitled, The Meaning of IN CHRIST in the Greek New Testament, he suggests 241 ways to translate it. I’ll list just a few:
by Christ – Ephesians 2:22
Christians – Romans 16:7
through Christ – Ephesians 1:9
because of Christ – Ephesians 1:7
in the service of Christ – Romans 16:12
under the authority of Christ – Ephesians 1:10
Hale points out that the meaning of in Christ is unclear in many contexts. For example, in Romans 16:9 – “Greet Urbanus our fellow worker in Christ” (NKJV), he suggests that in Christ could serve as an adjectival phrase to modify fellow worker, an adverbial phrase to modify greet, or a noun phrase to mean a Christian.
In my translation of this verse in The Better Life Bible, I convey the idea that in Christ identifies the common task of the fellow workers:
“Please give my greetings also to Urbanus,
who helps us tell others about Jesus.”