Love is the primary mark of Jesus' disciples. So fellowship between the disciples of Jesus is vital. In Matthew 18:18-20, we read of the power that results from such fellowship among the disciples of Jesus. A paraphrase of those verses would read something like this: The Lord Jesus said, "If two or three disciples of Mine are found in one place and have no disunity between them, but instead a unity like the symphony ("sumphoneo" (Greek) = agree) produced by a number of musical instruments playing together in harmony with each other, then I will be present in their midst. And then, if they ask My Father for anything, it will be granted to them. They will have authority to bind the workings of Satan in any place on earth; and whatever activities of Satan they bind here on earth, will be bound at their source in "the heavenlies" (from where these spirit-powers operate). Such believers will also have the power to deliver (loose) people who are bound by Satan on earth".
The devil knows the amazing power there is in unity and fellowship among Jesus' disciples, but many believers do not know it. And so Satan's main aim has always been to bring disunity among believers so as to make them powerless against him. What power there would be in a home, if the husband and wife were one in spirit! Satan would never be able to overcome such a home! What power there would be in a church if even two of its elders were one in spirit! Satan would never be able to overcome such a church! Satan triumphs over most Christian churches and homes, because such unity and fellowship is not found in them. I am not talking now about casting out demons. Any believer who has faith for this, can cast out demons in the Name of Jesus, single-handedly, as Jesus said in Mark16:17. In fact, we read in Matthew 7:22,23 of even unbelievers who cast out demons in Jesus' Name. But to bind the activities of Satan, so as to release people from the problems Satan has created for them is far more difficult. A believer cannot do that alone. That requires an expression of the Body of Christ - and the minimum number of disciples that can express Christ's Body is two! Only the authority exercised by such a "body" can keep the powers of darkness at bay.
There must be at least two people at the centre of every church who are totally united with each other. Satan will always target such a core seeking to split it up and divide it. If he succeeds, then that church will become powerless against him. But if that core keeps itself united, Satan will be powerless against that church. This applies to a home as well. In every church there will be mature people as well as new converts - just as there are babes as well as grown-up children in a family. The babes may fight with each other, backbite, complain and gossip, because they have not understood the way of peace. Such babes will be found in every growing church. But they can never hinder God's work. A core of united elders at the centre of a church can make it an overcoming church. Babes may constitute the vast majority of every church. But God is always seeking to build up the core - both spiritually and numerically. It is this core that fights the battles against Satan and preserves a church in life and victory. Fellowship in a church is more important than evangelism. In the parable of the lost sheep, Jesus said that the 99 sheep in the fold were "ninety-nine righteous persons who need no repentance" (Luke15:7). Who are the ones "who need no repentance"? Obviously those who are judging themselves constantly. Such people do not need any repentance, because they are constantly repenting of their sins. Such disciples have no problem becoming one with each other.