Shoghi Effendi was asked several times during his ministry to define the sphere of his operation and his infallibility. The replies he gave and which were written on his behalf are most illuminating. He explains that he is not an infallible authority on subjects such as economics and science, nor does he go into technical matters since his infallibility is confined to 'matters which are related strictly to the Cause'. He further points out that 'he is not, like the Prophet, omniscient at will', that his 'infallibility covers interpretation of the Revealed Word and its application', and that he is also 'infallible in the protection of the Faith'. Furthermore, in one of the letters, the following guideline is set forth:
"'... It is not for individual believers to limit the sphere of the Guardian's authority, or to judge when they have to obey the Guardian and when they are free to reject his judgment. Such an attitude would evidently lead to confusion and to schism. The Guardian being the appointed interpreter of the Teachings, it is his responsibility to state what matters which, affecting the interests of the Faith, demand on the part of the believers, complete and unqualified obedience to his instructions.