After Sri Ramakrishna had his mahasamadhi in 1886, Swami Vivekananda (at that time Narendranath) and some of his monastic brothers had gathered at Antpur, in December of that year. One night Swamiji sat with his brothers whole night before a fire and exhorted them to take Sannyasa in the tradition of great renunciates. In the morning they came to know it was Christmas Eve. Eventually they took Sannyasa, and the organisation was formed. In remembrance of that great beginning, Christmas Eve is treated as a sacred day by the monks and devotees of the Ramakrishna Sangha.
The language of the soul is one, the languages of nations are many; their customs and methods of life are widely different. Religion is of the soul and finds expression through various nations, languages, and customs. Hence it follows that the difference between the religions of the world is one of expression and not of substance; and their points of similarity and unity are of the soul, are intrinsic, as the language of the soul is one, in whatever peoples and under whatever circumstances it manifests itself. The same sweet harmony is vibrant there also, as it is on many and diverse instruments.
– Swami Vivekananda