“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)

Our individual and collective dependence on the “life and fortification of the Holy Spirit”

The world of humanity cannot advance through mere physical powers and intellectual attainments; nay, rather, the Holy Spirit is essential. The divine Father must assist the human world to attain maturity. The body of man is in need of physical and mental energy, but his spirit requires the life and fortification of the Holy Spirit. Without its protection and quickening the human world would be extinguished. Jesus Christ declared, "Let the dead bury their dead." He also said, "That which is born of the flesh is flesh; and that which is born of the Spirit is spirit." It is evident, therefore, according to Christ that the human spirit which is not fortified by the presence of the Holy Spirit is dead and in need of resurrection by that divine power; otherwise, though materially advanced to high degrees, man cannot attain full and complete progress. (‘Abdu'l-Baha, ‘The Promulgation of Universal Peace)

"Religion is the outer expression of the divine reality."

Religion is the outer expression of the divine reality. Therefore, it must be living, vitalized, moving and progressive. If it be without motion and nonprogressive, it is without the divine life; it is dead. The divine institutes are continuously active and evolutionary; therefore, the revelation of them must be progressive and continuous. (‘Abdu'l-Baha, The Promulgation of Universal Peace)

The “life of man must bring forth certain fruitage.”

The purpose of life is to get certain results; that is, the life of man must bring forth certain fruitage. It does not depend upon the length of life. As soon as the life is crowned with fruition then it is completed, although that person may have had a short life. There are certain trees which come to fruition very quickly, but there are other trees which attain to fruition very late; the aim is fruit. If the tree brings forth its fruit young, its life is short; it is praiseworthy. How regretful it is that a man may live a long life and yet his life may not be crowned with success, like unto the cypress tree which does not give any fruitage. (Words of ‘Abdu’l-Baha at the grave of Thornton Chase; Star of the West, vol.III, No. 13, November 4, 1912)