December 6

…one cannot be a Bahá'í and also a member of another religious organization. This is simply a matter of straight-forwardness and honesty. A great part of the teaching of Jesus Christ concerned His Second Coming and the preparation of His followers to be ready for it. The Bahá'ís believe He has come. No Christian Church believes this; on the contrary, they either look for Him still, or have ceased to believe that He will come. For a Bahá'í to be a member of a community which holds such beliefs is disloyalty to Christ and hypocrisy towards the Christians. 
- The Universal House of Justice  (From a letter of the Universal House of Justice to the National Spiritual Assembly of Switzerland, November 21, 1968: Canadian Bahá'í News Special Section, March 1973; compilation: ‘Lights of Guidance’)