In terms of the intensity of Their light and Its effect on the whole earth, previous Manifestations of God were like “stars”, and Baha’u’llah is like the “sun”

In cycles gone by, each one of the Manifestations of God hath had His own rank in the world of existence, and each hath represented a stage in the development of humanity. But the Manifestation of the Most Great Name -- may my life be a sacrifice for His loved ones -- was an expression of the coming of age, the maturing of man's inmost reality in this world of being. For the sun is the source and well-spring of light and heat, the focal point of splendours, and it compriseth all the perfections that are made manifest by the other stars which have dawned upon the world. Make thou an effort that thou mayest take thy place under the sun and receive an abundant share of its dazzling light. In truth do I tell thee, once thou hast attained this station, thou shalt behold the saints bowing down their heads in all humility before Him. Haste thou to life before death cometh; haste thou to the spring season before autumn draweth in; and before illness striketh, haste thou to healing -- that thou mayest become a physician of the spirit who, with the breaths of the Holy Spirit, healeth all manner of sickness in this famed and glorious age. ('Abdu'l-Baha, Selections from the Writings of 'Abdu'l-Baha, p. 56)