According to 2 John 10, we are not to receive into our homes or even greet anyone who comes to us and does not believe that Christ is come in the flesh. How does this apply to cultists? Should we turn them away?
I do not believe this verse prohibits Christians from allowing cultists into their homes in order to witness to them. Rather it is a prohibition against giving cultists a platform from which to teach false doctrine.
The backdrop to this is that in the early days of Christianity, there was no centralized church building where believers could congregate. Rather, there were many small house-churches scattered throughout the city.
As we examine the New Testament, the early Christians are seen "breaking bread from house to house" (Acts 2:46; cf. 5:42) and gathering to pray in the house of Mary, the mother of Mark (Acts 12:12). Churches often met in houses (see Col. 4:15; Rom. 6:15; 1 Cor. 16:19; Phil. 2). The use of specific church buildings did not appear before the end of the second century.
So, apparently, John is here warning against (1) allowing a false teacher into the church, and (2) giving this false teacher a platform from which to teach. Seen in this way, this prohibition guards the purity of the church. To extend hospitality to a false teacher would imply that the church accepted or approved of their teaching. If the church were to extend hospitality to a false teacher, he would be encouraged in his position and take this action as an acceptance of his doctrine. This should never be.
It is also possible that John may be forbidding Christians to allow false teachers to stay in their houses. It must be remembered that, in the early church, the evangelistic and pastoral ministry of the church was conducted primarily by individuals who traveled from location to location -- from house-church to house-church. These itinerant pastors depended on the hospitality of the people of a local congregation. John is directing the church not to extend this kind of hospitality to teachers of false doctrine. Christians are not to let cultists stay in their homes and use their homes as a base of operations from which to spread their poison and their false gospel.
In any case, this verse does not prohibit Christians from allowing cultists into the home for evangelistic purposes. When a Jehovah's Witness or a Mormon shows up on the doorstep, for example, the Christian should feel free to invite him or her into the living room in order to witness to them.
