It is noteworthy too that just as both institutions receive the same Divine care and protection, so the Guardian, by virtue of his membership, partakes of the authority vested in the House of Justice, although he has no individual legislative power.
These twin pillars of the World Order of Bahá'u'lláh, acting in close harmony, yet within clearly defined spheres, ensure the continuity of Divine guidance not only with respect to interpretation of the revealed Word, but also with respect to the practical application of the spiritual principles of the Faith to world affairs, as well as to legislative on those matters which Bahá'u'lláh has "deliberately left" out of "the body of His legislative and administrative ordinances" Authority therefore is vested in the House of Justice, according to the Will of Bahá'u'lláh and the Will and Testament of 'Abdu'l-Bahá. Guarantee, or guardianship, comes from the Guardian by virtue of his interpretation of the Word of God, the bedrock on which the whole structure is raised.
- Will and Testament of 'Abdu'l-Baha: A Commentary
by David Hofman published in Bahá'í World, Vol. 9 (1940-1944), pages 248-260