Prepositions are words that indicate position. There are not many of them, however they are very powerful words. The American phrase about government of the people, by the people, for the people, is memorable for its prepositions as much as for its propositions The Bible uses prepositions in that way. Here's just one example:
"All things have been created through him and for him, and he is before all things, and in him all things hold together"(Col 1:16-17).
Prepositions are powerful words because they express relationships. This may not be noticed in something commonplace, such as, "The log is in the fire". But how much is packed into one small word when we say, "The saved are in Christ".
Our entire relationship with God is very well expressed with three prepositions: We are in Christ,with Christ, and under Christ. That sounds like a slogan, and perhaps it is a slogan, and a very good one. Let's look at each of those prepositions and the relationships that they express.
In Christ
The first of our three prepositions is "in". The phrase "in Christ" was coined by Paul, and I think he must use it at least 100 times in his letters. I guess he took it from Jesus, who prayed for his disciples, "May they also be one in us... as we are one, I in them and you in me"(Jhn 17:20-23).
So the theme runs...
"All of you who were baptized into Christ... are all one in Christ Jesus"(Gal 3:26-29).
"There is now therefore no condemnation to those who are in Christ Jesus"(Rom 8:1).
"Christ in you, the hope of glory, whom we proclaim, that we may present everyone complete in Christ"(Col 1:27-28).
...and many other examples...
Union and Involvement
The preposition "in" expresses not only union, but intense involvement. We know what it is like when someone is "in love" don't we! If you are truly in Christ, you are taking up your cross daily (Lke 9:23-24).
With Christ
The second preposition in our threesome, is "with". Although it is not used as much as "in", there are some very forceful statements about us being with Christ. Here are some examples...
Jesus said, "He who is not with me, is against me"(Mtt 12:30).
He also said, "Lo I am with you always"(Mtt 28:18).
"Behold I stand at the door and knock. If anyone will hear my voice and open the door, I will come in to him, and sup with him, and he with me"(Rev 3:20).
Fellowship and Loyalty
The preposition "with" expresses not only fellowship but loyalty. We are with Christ when we are 'on the Lord's side'. If you are truly with Christ, you will "fight the good fight"(1Tm 6:12).
Under Christ
The third preposition of the three is "under". It is used least of all, yet still packs a punch. Here are some examples...
"You are no longer under a schoolmaster"(Gal 3:24-25).
"You are not under law but under grace"(Rom 6:14).
"God has put all things in subjection under his feet"(1Co 15:25-28, Eph 1:22).
"Humble yourselves therefore under the mighty hand of God"(1Pe 5:6).
Submission and Protection
Being "under" Christ means recognising his sovereignty, not only in word but also in deed, as he himself says, "Why do you call me Lord, Lord, and do not do what I say?"(Lke 6:46). Speaking of our being under Christ expresses our submission and obedience to him as his bondslaves. However there is also the idea of protection. When we are under Christ, we have a ward against evil because we are under his care and protection from the evil one. To use the lovely Old Testament metaphor, we are "under his wings to seek refuge"(Rth 2:12, Psa 17:8).