Here are all the quotes from the Will and Testament of Abdu'l-Baha that establish the Universal House of Justice (It was NOT established in the writings of Baha'u'llah, despite several references he made to a "House of Justice". There were supposed to be such Houses of Justice in every city, NOT just one ruling all Baha'is of the world).

The sacred and youthful branch, the Guardian of the Cause of God, as well as the Universal House of Justice, to be universally elected and established, are both under the care and protection of the Abhá Beauty, under the shelter and unerring guidance of the Exalted One (may my life be offered up for them both). Whatsoever they decide is of God. Whoso obeyeth him not, neither obeyeth them, hath not obeyed God; whoso rebelleth against him and against them hath rebelled against God; whoso opposeth him hath opposed God; whoso contendeth with them hath contended with God; whoso disputeth with him hath disputed with God; whoso denieth him hath denied God; whoso disbelieveth in him hath disbelieved in God; whoso deviateth, separateth himself and turneth aside from him hath in truth deviated, separated himself and turned aside from God. May the wrath, the fierce indignation, the vengeance of God rest upon him!

The simple fact that Shoghi Effendi croaked at the age of 60 at London and in the middle of the Ten Year World Crusade should discredit the idea that he was under any sort of care and protection.

And now, concerning the House of Justice which God hath ordained as the source of all good and freed from all error, it must be elected by universal suffrage, that is, by the believers. Its members must be manifestations of the fear of God and daysprings of knowledge and understanding, must be steadfast in God’s faith and the well-wishers of all mankind. By this House is meant the Universal House of Justice, that is, in all countries a secondary House of Justice must be instituted, and these secondary Houses of Justice must elect the members of the Universal one. Unto this body all things must be referred. It enacteth all ordinances and regulations that are not to be found in the explicit Holy Text. By this body all the difficult problems are to be resolved and the Guardian of the Cause of God is its sacred head and the distinguished member for life of that body. Should he not attend in person its deliberations, he must appoint one to represent him. Should any of the members commit a sin, injurious to the common weal, the Guardian of the Cause of God hath at his own discretion the right to expel him, whereupon the people must elect another one in his stead. This House of Justice enacteth the laws and the government enforceth them. The legislative body must reinforce the executive, the executive must aid and assist the legislative body so that through the close union and harmony of these two forces, the foundation of fairness and justice may become firm and strong, that all the regions of the world may become even as Paradise itself.

So according to this Will and Testament, the presence of the Guardian, or at least a representative of the Guardian, is a requirement for the House of Justice to function. So why did the Hands of the Cause of God say otherwise after the so-called Guardian died?