"That which is born of the flesh is flesh; and that which is born of the Spirit is spirit"(John 3:6) – explanation by ‘Abdu’l-Baha

Christ announced, "That which is born of the flesh is flesh; and that which is born of the Spirit is spirit," meaning that man must be born again. As the babe is born into the light of this physical world, so must the physical and intellectual man be born into the light of the world of Divinity. 
('Abdu'l-Baha, The Promulgation of Universal Peace)