In Ephesians 3:4-6 Paul speaks of his understanding of the mystery of Christ. This mystery was not made known to the sons of men in other generations. The men of old did not know of the mystery that God spoke through Paul, which involves the Jews and Gentiles becoming one new man in Christ Jesus. This is the corporate Christ, which is the church. Verse 6 of chapter three is a precious verse. The words "fellow members" refer to the new man in Ephesians 2:15. The new man stands in contrast to the old man. There are many individual men in this world, but there is only one old man. In the same way, there are many Christians, but there is only one new man—the church.
In order to understand what the new man is, we must first understand what the old man is. The old man is the God-created man who fell through sin. Every person in Adam is not only a sinner before God, but also an old man. When such a sinner, the old man, hears the gospel and believes in Christ and is saved, he becomes a new man. Not only has he become a new man individually; he is joined to all other Christians to become one corporate new man as well. Ephesians 1 speaks of the church as the Body of Christ; chapter two speaks of the church as the new man; chapter three speaks of the mystery of Christ; chapter four speaks of the way to build up the Body of Christ; chapter five speaks of the responsibility of the church; and chapter six speaks of the warfare of the church. The peak of God's work is the church, which is the new man. God saves us so that we will become a new man in Christ.
A great lack among Christians today is that everyone wants to be an individual Christian. Everyone wants to be good and zealous; everyone wants to sit and listen to good sermons. In short, everyone wants to be a Christian in an individual way. But God does not just want us to be good on an individual basis. He is after a corporate vessel that will destroy Satan and accomplish His plan. God does not want to see Christians scattered like a pan of sand. He wants Christians to be joined together to become a corporate new man.
Ephesians 2 speaks of Christ creating one new man out of two groups of people, but it does not tell us what the new man is like. According to Colossians 3:10-12, the new man is renewed unto full knowledge according to the image of Him who created him. In the new man there is no Greek or Jew, circumcision or uncircumcision, barbarian or Scythian, slave or free man, but Christ is all and in all. The new man is not a matter of having or not having distinctions; it is a matter of either being the new man or being nothing. The new man is not in the realm of being a Greek or a Jew. The new man is simply Christ. The nature of the new man is Christ. In the new man Christ is all and in all. We can even venture to say that Christ is the church and the church is Christ, because everything in the new man—the church—is simply Christ. The constitution of the new man is nothing less than Christ Himself.