Under the new covenant, God has not intended that we should be lone Christians living by ourselves - even if we are living in victory over sin. God's will is that there should be a Body of disciples of Jesus manifesting His glory together.
There is a difference between a Body and a congregation. A congregation is no better than a secular club. The club may be a good club, where people care for one another and help one another. But a Body is more than that. In the Body of Christ, each member is first of all inwardly connected to the Head and then inwardly and inseparably connected to the other members. These members must grow in oneness until their unity is like the unity of the Father and the Son (Jn.17:21-23).
Satan opposes the building of such a Body anywhere on earth, for he knows that such a Body can rout him, put him to flight, and destroy his kingdom. Jesus said that it is against the church that the gates of Hell would not prevail (Matt.16:18). The gates of Hell may prevail against a lone individual Christian. But they cannot prevail against the church. That is why Satan's attacks on spiritual unity among believers are far stronger than his attacks on purity.
Where any two disciples of Jesus are firmly united in oneness of mind and spirit, whatever they ask for will be granted, for in two such disciples is found an expression of the Body of Christ (Matt.18:18-20).
In fellowship with other believers, we will discover the selfishness and utter corruption of our flesh much more quickly and more deeply than if we lived all by ourselves. It is only through fellowship with others who have a flesh that our rough edges can be smoothened out.
Many believers merely spin theories about the church and the Body of Christ. But we must be among those who seek reality. There are enough theories about the church in Christendom. We don't have to add to that number with one more theory or doctrine about the Body of Christ. Let us demonstrate the reality of the Body in our mutual relationships in our local church, and thus demonstrate to the world and to Satan that the Body of Christ is a reality on earth.