Progress is of two kinds, material and spiritual. The former is attained through observation of the surrounding existence and constitutes the foundation of civilization. Spiritual progress is through the breaths of the Holy Spirit and is the awakening of the conscious soul of man to perceive the reality of divinity. Material progress insures the happiness of the human world. Spiritual progress insures the happiness and eternal continuance of the soul. The prophets of God have founded the laws of divine civilization. They have been the root and fundamental source of all knowledge. They have established the principles of human brotherhood or fraternity which is of various kinds, such as the fraternity of family, of race, of nation and of ethical motives. These forms of fraternity, these bonds of brotherhood are merely temporal and transient in association. They do not insure harmony and are usually productive of disagreement. They do not prevent warfare and strife; on the contrary they are selfish, restricted and fruitful causes of enmity and hatred among mankind. The spiritual brotherhood which is enkindled and established through the breaths of the Holy Spirit unites nations and removes the cause of warfare and strife. It transforms mankind into one great family and establishes the foundations of the oneness of humanity. It promulgates the spirit of international agreement and insures Universal Peace. Therefore we must investigate the foundation reality of this heavenly fraternity. We must forsake all imitations and promote the reality of the divine teachings. In accordance with these principles and actions and by the assistance of the Holy Spirit, both material and spiritual happiness shall become realized. Until all nations and peoples become united by the bonds of the Holy Spirit in this real fraternity, until national and international prejudices are effaced in the reality of this spiritual brotherhood, true progress, prosperity and lasting happiness will not be attained by man. This is the century of new and universal nationhood. Sciences have advanced, industries have progressed, politics have been reformed, liberty has been proclaimed, justice is awakening. This is the century of motion, divine stimulus and accomplishment; the century of human solidarity and altruistic service; the century of Universal Peace and the reality of the divine kingdom.
— ‘Abdu’l-Baha, Baha’i World Faith, pp. 227 – 228