June 23

They [Bahá'u'lláh and 'Abdu'l-Bahá] have also, in unequivocal and emphatic language, appointed those twin institutions of the House of Justice and of the Guardianship as their chosen Successors, destined to apply the principles, promulgate the laws, protect the institutions, adapt loyally and intelligently the Faith to the requirements of progressive society, and consummate the incorruptible inheritance which the Founders of the Faith have bequeathed to the world. 
(Shoghi Effendi, from a letter of 21 March 1930, published in ‘The World Order of Bahá'u'lláh - Selected Letters’; The Compilation of Compilations, vol. I, The Covenant)