Spiritism

Not to join religious or political associations like Spiritism even if there are some good points in it, as can't reconcile teachings of the Faith with all views of any existing group; disassociate gradually so as not to arouse antagonism

"...the Guardian feels it incumbent upon him to make it quite clear that membership in every Bahá'í organization excludes the possibility of joining any religious or political association, even though such an alliance does not involve a complete repudiation of Bahá'í principles and doctrines. It would be utterly impossible to reconcile the teachings of the Faith with all the views and conceptions which any existing group, whether religious or political, may advocate. In view of that, it seems but logical that a Bahá'í cannot be a spiritist at the same time. Not that the ideas which the spiritists proclaim are each and all in direct opposition to the Bahá'í teachings. As a matter of fact there are some good points in spiritism. But this is not sufficient justification for a believer to accept membership in a spiritist organization.

"While Shoghi Effendi would urge you to dissociate yourself from the spiritists, he wishes you at the same time to act with caution and wisdom. Your separation from the spiritists should be gradual, and in a way that would not arouse the antagonism of your friends and relatives. Too sudden and abrupt a change is, indeed, harmful not only to you but to those who through you have been attracted to the Cause...."

(From a letter written on behalf of Shoghi Effendi to an individual believer, April 14, 1934, in Lights of Guidance, no. 1399)