The infallibility of the Guardian is confined to matters which are related strictly to the Cause and interpretation of the teachings; he is not an infallible authority on other subjects, such as economics, science, etc. When he feels that a certain thing is essential for the protection of the Cause, even if it is something that affects a person personally, he must be obeyed, but when he gives advice, such as that he gave you in a previous letter about your future, it is not binding; you are free to follow it or not as you please.

Shoghi Effendi, Directives from the Guardian, p. 33-34

From the above extracts it seems fairly clear that letters written on behalf of Shoghi Effendi "related strictly to the Cause and interpretation of the teachings" constitute authoritative Bahá’í text, while any personal advice which they may contain is not binding. The Guardian's statement that he reviewed every letter written on his behalf without exception makes it clear that the authority of the letters was independent of whatever personal "sufferings" might have been caused by certain secretaries, and that there was no "delegation" whatsoever of his interpretative authority, but merely a use of secretarial assistance for his huge burden of correspondence.

The Universal House of Justice, 1996 Oct 22, Authentication and Authority

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.

Universal House of Justice, Lights of Guidance, p. 311

The Universal House of Justice in arriving at a decision needs to have before it all the facts involved in the matter. If, after making a decision, new facts emerge, it may well be changed

Letter on behalf of the Universal House of Justice, dated 13 August 1981

With regard to decisions taken by the Universal House of Justice itself, instructions it issues, and the relationship of these to the information supplied, it is obvious that the nature of a decision or instruction is affected by the information on which it is made.

Letter on behalf of the Universal House of Justice, dated 26 May 1993

Your first question stems from a statement made by an individual on an Internet Bahá’í discussion group which asserts that "Shoghi Effendi has allowed for the Universal House of Justice reaching a wrong decision." In describing the House of Justice, ‘Abdu’l-Bahá states clearly, “Whatever will be its decision, by majority vote, shall be the real truth, inasmuch as that House is under the protection, unerring guidance and care of the one true Lord. He shall guard it from error and will protect it under the wing of His sanctity and infallibility. He who opposes it is cast out and will eventually be of the defeated. It is the exclusive sphere of the Universal House of Justice to "pronounce upon and deliver the final judgment on such laws and ordinances as Bahá’u’lláh has not expressly revealed." It carries responsibility for the application of the revealed Word, the protection of the Faith, as well as the duty "to insure the continuity of that divinely-appointed authority which flows from the Source of our Faith, to safeguard the unity of its followers and to maintain the integrity and flexibility of its Teachings." However, the Universal House of Justice is not omniscient, and the friends should understand that there is a difference between infallibility and omniscience. Like the Guardian, the House of Justice wants to be provided with facts when called upon to render a decision, and like him it may well change its decision when new facts emerge, or in light of changed conditions at some point in the future. We have found nothing in the writings of Shoghi Effendi which suggests that the House of Justice would on any occasion reach a "wrong decision".

The Universal House of Justice, 1996 Jun 14, Infallibility, Women on House of Justice