2 Corinthians 5:17a, “Therefore, if anyone is in Christ, he is a new creation….” “In Christ” is one of Paul’s favorite ways of understanding the New Creation and describing what it is to be a Christian. The best way to understand what it means to be in Christ is by comparing it to the phrase in Adam. 1 Corinthians 15:22, “For as in Adam all die, so also in Christ shall all be made alive.”
Paul teaches that there really are two kinds of human beings on the earth now: the old people who are in Adam—and we all are born to this world in Adam—and the New Creation people who are in Christ. Those who are born again of the Holy Spirit are now no longer in Adam, they are in Christ! When you believe in the Lord Jesus Christ you are now “in” Christ.
As Adam was the head and representative of the old humanity; so Christ is the head and representative of the new humanity. In Adam brought us sin, disobedience, condemnation and death. In Christ brought us righteousness, obedience to God, acquittal, life, and a New Creation.
Those who are in Adam belong to the old age with it’s bondage to sin and death and is passing away; but those who are in Christ belong to the “real” new age of God’s Kingdom with all of it’s righteousness and life.
So, to be a New Creation in Christ means being a participant in a new age and realm of God’s salvation–experiencing now a piece of all that heaven will ultimately swallow the entire universe with! If we are in Christ, we really are an entirely new created order of things. We are the first fruits of all of the newness of heaven that will ultimately overtake the entire created universe. To be in Christ points to what is to come in Ephesians 2:10b, “to unite all things in him, things in heaven and things on earth.”