“The proof of the validity of a Manifestation of God ..”

The proof of the validity of a Manifestation of God is the penetration and potency of His Word, the cultivation of heavenly attributes in the hearts and lives of His followers and the bestowal of divine education upon the world of humanity. This is absolute proof. The world is a school in which there must be Teachers of the Word of God. The evidence of the ability of these Teachers is efficient education of the graduating classes. ('Abdu'l-Baha, The Promulgation of Universal Peace, p. 340)