Today the world of humanity is in need of international unity and conciliation. To establish these great fundamental principles a propelling power is needed. It is self-evident that the unity of the human world and the Most Great Peace cannot be accomplished through material means. They cannot be established through political power, for the political interests of nations are various and the policies of peoples are divergent and conflicting. They cannot be founded through racial or patriotic power, for these are human powers, selfish and weak. The very nature of racial differences and patriotic prejudices prevents the realization of this unity and agreement. Therefore, it is evidenced that the promotion of the oneness of the kingdom of humanity, which is the essence of the teachings of all the Manifestations of God, is impossible except through the divine power and breaths of the Holy Spirit. Other powers are too weak and are incapable of accomplishing this.
All the Prophets have come to promote divine bestowals, to found the spiritual civilization and teach the principles of morality. Therefore, we must strive with all our powers so that spiritual influences may gain the victory. For material forces have attacked mankind. The world of humanity is submerged in a sea of materialism. The rays of the Sun of Reality are seen but dimly and darkly through opaque glasses. The penetrative power of the divine bounty is not fully manifest.
Abdu'l-Bahá, The Promulgation of Universal Peace