There are two movements of Israel described in great detail in the Old Testament.
The movement from Egypt to Canaan symbolises our Individual life - coming out of sin, out of Satan's grip and out of the world, through the blood of Christ, water-baptism and the baptism in the Holy Spirit, into a life of victory over sin and a personal walk with God.
The movement from Babylon to Jerusalem symbolises our corporate life - leaving counterfeit Christendom and coming into a genuine expression of the Body of Christ.
Many Christians think that Babylon refers to certain denominations in Christendom and imagine that once they have left those dead denominations they have left Babylon. This is not true.
Babylon is a commercial system. The principle of all commercial systems is profit - gain for oneself. As long as a man is living by the principle of "personal gain through Christianity" - What he can gain by doing something for the Lord, What he can gain by joining a church or organization, etc., - he is motivated by the principle of Babylon.
A Christian, who lives after the flesh and seeks his own, even if he is in the best denomination in the world, is still a part of Babylon. The spirit of Babylon is found primarily within a man, and not primarily in a denomination.
Jerusalem however is a city of sacrifice. Its spirit is the opposite of the business spirit found in Babylon. It is the spirit found in the words of David when he said, "I will not offer to the Lord that which costs me nothing" (2 Sam.24:24).
To build the body of Christ - "the heavenly Jerusalem" - requires such a selfless spirit that is concerned about the glory of God alone, and that does not seek one's own. And a person with such a spirit may be found at times even in a dead denomination. For the spirit of Jerusalem too is primarily an inward thing, and not an outward matter.
If we seek to build the Body of Christ, it is important that we gather together those who have understood this principle of sacrifice. Otherwise we shall build another system like the old one. This is what many of the so-called �separated assemblies' have done, and they are now just as dead (or more dead) than the mainline denominations.