Abarim Publications' online Biblical Greek Dictionary
There are two different prepositions spelled εν, namely εν (en), meaning in, and εν (hen), meaning one. The latter is the neutral form of the cardinal number εις (heis), meaning one.
The preposition εν (en) appears as leading element of a colossal array of words. It roughly works the same as the English preposition "en-" (as in words like: entrance, enthuse, enslave), although in Greek it's much more commonly and broadly used than in English. The nature of the action that this particle describes (to or toward) provokes the dative case.
The familiar phrase 'in Christ' employs this particle, and it demonstrates that our belief 'in Christ' does not entertain Christ as the subject of our faith but rather the environment in which we perform our faith (we believe in Christ the way we dance in the rain). Our believing is done within the reality of Christ, and the subject of our faith is not Christ but rather "all things" (Matthew 11:27, Romans 11:36, 1 Corinthians 13:7, Colossians 1:16-17; see our article on πιστις, pistis, meaning faith, or our elaborate "statement of faith" for more on this).
Our particle is used whenever we're in a place or building, on an elevation, amidst a multitude, in someone's presence, at someone's feet, enveloped by something, in a certain time period, in a certain situation, under a certain condition, in a certain way, under a certain influence, with the help of something.
Our preposition generally means in, at or by and expresses a situation either inside something or endowed with something, but always at rest — this in contrast to the more motive prepositions εις, eis, meaning into, and εκ, ek, meaning out of.
In the rare cases in which this preposition is used with verbs of motion, the use of εν (en) implies that we're looking at a situation that results from a motion inward, instead of the actual movement.
The preposition εν (en) is used 2795 times in the New Testament; see full concordance.
From our particle εν (en), meaning in, comes the adverb εντος (entos), meaning innerly or inwardly, or when used substantially: the inside, as opposed to εκτος (ektos), outerly or the outside. Our adverb εντος (entos) is used only twice in the New Testament. Once it denotes the inside of cups and dishes (Matthew 23:26), and once it occurs in Jesus' assertion: the kingdom of God is within you (Luke 17:21). This is often explained to refer to people's internal sentiments, but it doesn't. The word for "you" is in plural. If Jesus had wanted to say that the kingdom of God is an internal and personal emotional matter he would have forced a singular form: within each of you. Now he says that the kingdom of God is a matter of social cohesion and social networking.
The gospel is not about personal enlightenment but about collective understanding. It's not about spacey energies and divine sparks but about a calm, conscious, intellectual and most of all a shared and confirmed knowledge of nature (Romans 1:20, Colossians 2:3) and the living currency of a love that surpasses all knowledge but is still very much focused on others (Ephesians 3:19).
The gospel is not about mastery of passions and lusts but about an intimate communion with natural law (Colossians 1:16-17). The result of knowing these laws (beside hence knowing the Creator of those laws) is freedom within a closely knit society (Galatians 5:1); a perfect society in which everybody is free and God lives openly and wholly recognized among mankind (John 1:14, Revelation 21:23). The entire law and the prophets depend on loving the Creator wholly and one's neighbor as oneself (Matthew 22:37-40). The afterlife consists of a physical and earthly resurrection, and a blissful state of private nirvana is not part of the Biblical dealio.