The NDFs are for the Bahá'ís, and the Bahá'ís exclusively, and no variation from this principle is permitted."The beloved Guardian has instructed me to write you concerning an action recently taken by your National Assembly, as published in your January-February Bahá'í News, that non-Bahá'ís may attend 19 Day Feasts if 'the earnestness of their interest in the Faith' is vouched for by a declared believer.
"The Guardian wishes me to direct your attention to the fact that none of the institutions of the Faith nor its cardinal principles may be changed under any circumstances.
"The 19 Day Feast is an institution of the Cause, first established by the Bab, later confirmed by Bahá'u'lláh, and now made a prominent part of the administrative order of the Faith. These 19 Day Feasts are for the Bahá'ís, and the Bahá'ís exclusively, and no variation from this principle is permitted.
"Thus the Guardian feels you should rescind the action taken by your Assembly in opening the Feasts to 'near Bahá'ís', as it is not consistent with the spirit of the administrative order for non-Bahá'ís or near Bahá'ís to attend the 19 Day Feasts, particularly the administrative portion of the Feast."
(From a letter written on behalf of the Guardian to the National Spiritual Assembly of Germany and Austria, May 28, 1954: The Nineteen Day Feast, November 1975)