'This verse reminds us that the Gospel has its intolerance as well as tolerance' (Bp. Alexander). Ordinary courtesy is not forbidden, but to extend the right hand of fellowship would be to condone and further false doctrine and to share the guilt of disloyalty.
Related Commentaries of 2 John 1:10
2 John 1:10
10 If there come any unto you, and bring not this doctrine, receive him not into your house, neither bid him God speed: