“The seriousness of Covenant-breaking is that it strikes at the very center and foundation of the unity of mankind. If God were to allow the instrument to be divided and impaired, how then would His purpose be achieved?
… The believers are commanded to shun Covenant-breakers for the same reason as healthy people do not associate with a person suffering from a serious contagious illness. A contagiously sick person cannot catch health from a thousand healthy people, but, on the contrary, he can infect them with his illness. Therefore such a person is quarantined and only those few people qualified to attend him do so. . . . Then, if he proves adamant he is free to go his way, but the Bahá’ís must cease to have any association with him until such time as he repents when, of course, he can be accepted back into the community.”
The Universal House of Justice, March 23, 1975, Developing Distinctive Bahá’í Communities.