Abdu'l-Baha, The Will and Testament

O my loving friends! After the passing away of this wronged one, it is incumbent upon the Aghsan (Branches), the Afnan (Twigs) of the Sacred Lote-Tree, the Hands (pillars) of the Cause of God and the loved ones of the Abha Beauty to turn unto Shoghi Effendi -- the youthful branch branched from the two hallowed and sacred Lote-Trees and the fruit grown from the union of the two offshoots of the Tree of Holiness, -- as he is the sign of God, the chosen branch, the Guardian of the Cause of God, he unto whom all the Aghsan, the Afnan, the Hands of the Cause of God and His loved ones must turn. He is the Interpreter of the Word of God and after him will succeed the first-born of his lineal descendants.

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 Abha 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…

~Abdu'l-Baha, The Will and Testament